bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Study on Cavitation Motion of Underwater Vehicle With Protrusions
Authors: Qu Zhaoyu , Gan Ning , Chen Yingyu , Yang Nana
Published: December 2020

For underwater vehicles with protrusions (external structure), the geometric shape of the protrusions is bound to affect the local flow field of the vehicles during the moving process of the vehicles, thus affecting the generation, development and collapse of cavitation around the vehicles. The cavitation may break, fall off and collapse randomly, and other local movements may affect the motion attitude of the underwater vehicle. It is an effective method to study fluid dynamics to simulate prototype cases with small scale models. In this paper, we mainly use the small scale model test method to explore the cavitation motion characteristics of the vehicle in water with protrusions. Through the establishment of a set of vehicle motion test equipment under reduced pressure, a series of experiments were conducted on this basis to explore the motion characteristics of vehicle cavitation under different bump shapes. In this study, two high-speed cameras were used to simultaneously record cavitation generation, development, collapse and other characteristics, to analyze the bubble generation mechanism and scale characteristics caused by the bulge, and then to study the influence of cavitation induced by the bulge on the motion attitude of the vehicle.
Development of a 10-MW Semisubmersible Type Floating Offshore Wind Turbine for the East Sea, Korea
Authors: Ahn Hyeonjeong , Shin Hyunkyoung
Published: December 2020

The area of renewable energy is expanding rapidly worldwide, with wind turbines being an example. In Korea, many researchers are conducting studies on floating offshore wind turbines (FOWTs) on areas with suitable wind resources. In particular, Ulsan, which is the site selected in this study, started research on the development of a 200-MW floating offshore wind farm. In this study, the references for upscaling are the 5-MW reference wind turbine of the National Renewable Energy Laboratory (NREL), and the OC4-DeepCwind semisubmersible type floating wind turbine. We upscaled the 5-MW wind turbine to a 10-MW FOWT by applying the appropriate scale ratio for each component of the turbine. We upscaled the specifications related to items such as the blades, hub, and nacelle using the power ratio. The mass of the blades was reduced by using carbon fiber-reinforced plastic (CFRP). We upscaled the specifications related to the tower using its deflection ratio, and the tower clearance criterion and the tower campbell diagram were used to confirm that the design is appropriate. We upscaled the specifications related to the platform using the upper structure mass ratio. The GZ curve of the platform was used to confirm the stability, and we used the air gap for safety. Three catenary type mooring lines were also designed. To understand the static response of the initial model of the 10-MW FOWT, a steady-state analysis was performed according to each wind speed. We followed the IEC and DNV standards, and we used NREL FAST in all simulations.
Assessing RANS Numerical and Modeling Properties in the Simulation of the Flow Around Captive and Moving Cylinders
Authors: Costa Rita M. , Eça Luís , Koop Arjen
Published: December 2020

In many Engineering applications, the Reynolds-Averaged Navier-Stokes (RANS) equations are still used to simulate high Reynolds numbers (turbulent) flows around complex geometries. In flows that exhibit significant regions of flow separation leading to vortex shedding, it does not make sense to define the mean flow using time-averaging. Therefore, the use of RANS (even if locally) in statistically unsteady flows requires the application of ensemble-averaging to the flow variables and to the mass and momentum equations, which generates the appearance of the Reynolds stresses. Turbulence models available in the open literature have been developed for the simulation of statistically steady flows (mean flow defined by time-averaging). Nonetheless, the same models are used for the simulation of statistically unsteady flows. Therefore, it is not guaranteed that such models provide sufficient diffusion (damping) to capture only the mean flow.

In this paper, we have investigated the modeling and numerical properties of RANS supplemented by the k–ω SST eddy-viscosity model when applied to the classical problem of the flow around captive and moving (imposed motion) cylinders with Reynolds numbers ranging from 102 to 106. Two and three-dimensional simulations are performed and numerical (statistical, iterative and discretization) convergence properties are assessed for moving and deforming grids techniques. The quantities of interest are the drag and lift coefficients, for which we determine the frequency content of the time signal to assess if the numerical results correspond (as intended) to the mean flow. Results obtained at a Reynolds number of 104 are compared with experimental data available in the open literature.
CFD-Based Operation Optimization of Hybrid Ships
Authors: Guo Bingjie , Vartdal Bjørn-Johan , Alnes Øystein Åsheim
Published: December 2020

Hybrid propulsion technology is interesting for shipping, both due to possible reduction in fuel cost and strict emission regulations. The efficiency of a hybrid propulsion system will however depend on the power system configuration and the choice of power and energy management strategies. In this study, a simulation model is developed based on CFD, to investigate power management strategies of hybrid propulsion during transit operation. Two engineering operation approaches using fixed RPM mode and fixed power mode are simulated, in order to investigate power management strategy of the hybrid propulsion system. The transition operation of offshore supply vessel Viking Lady is used as an investigated object in the present study. The numerical simulations are performed in both regular sea and irregular sea. CFD results show that the models with the fixed RPM mode and the fixed Power mode give similar results in the power consumption, provided that the ship resistance in waves is predicted accurately as well as the output power and propeller revolution rate are properly designed. The model with the fixed RPM was expected to be able to reduce the power consumption by minimizing ship speed fluctuations when running in heavy sea conditions. The present numerical results show that the fixed RPM mode tried to reduce ship speed change by changing output power. However, it is not able to reduce the change of ship speed efficiently when the first-order wave forces are significantly large, and the power consumption is consequently not reduced.
An Optimization Method for Economical Ship-Routing and Ship Operation Considering the Effect of Wind-Assisted Rotors
Authors: Sun Wenyu , Liu Xiyang , Yang Li
Published: December 2020

With the increasingly strict regulations for energy saving and emission reduction technology of ships, minimizing fuel cost is one of the most critical issues in the design and operation of merchant ships. A method to reduce the fuel cost for merchant ship is to select an economical route based on the real-time meteorological environment and weather forecasting data. So far, numerous ship routing strategies have been proposed with the development of weather routing system. More recently, many wind-assisted devices like rotors, wind sails, etc. have been investigated and designed to utilize the renewable wind energy. With the equipment of wind-assisted rotors, the optimization of ship route becomes more important because the effect of this wind-assisted device highly depends on the local wind field along the ship route. In this paper, an improved optimization strategy with the combination of the A* algorithm and a realtime optimizer has been proposed to determinate the optimal ship route and ship operations including ship heading, propeller’s rpm and rotor’s rpm. The real-time information for the weather conditions, ocean climate and sea states are obtained from European Center for Medium-range Weather Forecasts and the ship performance is evaluated by data-driven models. Finally, the proposed method was applied to test cases of ships operating in Pacific route and Indian Ocean route and the results show that the total fuel consumption could be reduced compared to the minimum distance route.
Numerical Trials for the Soil-Spudcan Interface of Self-Elevating Units
Authors: Alegre F. , Logarzo J. , Alibakhshi S. , Achard A.
Published: December 2020

This paper describes the development of a numerical model of a jack-up leg supported on the seabed and the study performed in order to analyze the interaction at the interface between the soil and its spudcan.

Self-elevating units or jack-ups are widely used for offshore operations and the strength of their whole structure is to be ensured for the environmental conditions encountered during the operations. This is why the determination of the soil-spudcan interface is a major challenge since it depends on a wide range of factors, such as sea conditions, properties of the soil, geometry and material of the structure, etc.

In light of the unpredictable and non-linear behavior of the marine environment and the soil, it is necessary to develop further studies on this subject to reduce uncertainties and to ensure the safety of offshore structures, as most of the failures in the offshore oil platforms are related to foundations.

To do so, different approaches have been used:

• Abaqus/ Standard and Abaqus/Explicit solvers;

• Rigid bodies and deformable bodies afterwards;

• Three kind of meshes:

○ Lagrangian mesh;

○ Arbitrary Lagrangian - Eulerian mesh;

○ Coupled Eulerian - Lagrangian mesh.

To validate the model and the results obtained numerically in the end of the project, a comparison with an analytical calculation of the spudcan penetration has to be performed, based on the geometry of the structure and the properties of the soil.
Numerical Investigation of Scour Beneath a Subsea Piggyback Pipeline
Authors: Huang Jun , Yin Guang , Ong Muk Chen , Jia Xu
Published: December 2020

In present study, two-dimensional numerical simulations have been carried out to investigate scour beneath a piggyback pipeline subjected to a subsea boundary layer flow using SedFoam (an open-source multi-dimensional Eulerian two-phase solver for sediment transport based on OpenFOAM). In the piggyback configuration, a small pipeline is attached on the upstream and downstream sides of a large pipeline. This form of piggyback can reduce the scour depth beneath the pipeline (Yang et al., 2019). In the solver, the turbulence Reynolds stress is resolved using a two-phase modified k-ε model. The particle stresses caused by the binary collisions and contacts are modeled by the kinetic theory for granular flow and a phenomenological frictional model, respectively. The effects of the locations of the small pipelines attached on the large pipeline on the scour and the surrounding flow field are discussed.
Study on the Structural Safety Evaluation of the Self-Elevating Offshore Wind Turbine Installation Platform
Authors: Jiayi Hou , Yu Li , Haihua Zhang , Tiantian Kan
Published: December 2020

In order to accurately evaluate the influencing factors of the structural safety of the self-elevating offshore wind turbine installation platform, the load in the standing operating state and towing state is studied in this paper, which includes self-gravity load, wind load, current load, wave load, wave-induced inertia force, dynamic amplification load and operating load. This paper focuses on two working states of the platform. In the standing state, the effect of environmental load, as well as the dynamic amplification load is considered under both normal operating condition and storm condition. In the towing state, mainly the wave environmental load is taking into consideration. According to the data calculated above, the strength calculation is carried out. The results show that the design strength of the platform meets the requirements. This calculation method can provide a basis for the design of the self-elevating platform.
Experimental Investigation on a Point Absorber Moored by Taut Mooring System and Mooring Fatigue Analysis
Authors: Xu Sheng , Guedes Soares C.
Published: December 2020

In this paper, a taut wire mooring system has been designed consisting of three wire ropes symmetrically arranged. The power take-off system is modelled by a linear spring and a heave plate to simulate the linear damping of the power take-off. A series of regular wave tests in head seas are performed to study the dynamics of the system. Irregular wave tests were then conducted to simulate the system performance in the operational sea states, where the irregular waves are modelled by the Jonswap spectrum. The WEC motion responses and mooring tensions are studied. The short term mooring fatigue damage estimated by different spectral methods are compared to the rainflow counting method. The spectral method for estimating fatigue damage include the Dirlik formula, Jiao-Moan method and Tovo-Benasciutti approach. The accuracy of spectral methods for predicting mooring fatigue damage are discussed.
Space-Time Statistics via Trapezoidal Storm Model for Offshore Installations
Authors: Laface Valentina , Romolo Alessandra , Bitner-Gregersen Elzbieta M.
Published: December 2020

The paper proposes an approach for estimating the long-term statistics of random wave crests occurring over a certain space–time domain. Such a problem is relevant for a number of marine engineering applications, as classical analyses based, exclusively, on time domain approaches underestimates wave crest amplitudes associated with a given return period. The return period of a certain wave crest is derived by combining the Trapezoidal Storm (TS) Model, based on DNV GL storm profile, with the Euleric Characteristic (EC) of an excursion set concept, recently applied to the study of sea wave statistics. By computing the average EC, an explicit solution for the probability distribution of the wave crests during a sea storm can be derived by an approximation of the EC. Return period of linear wave crests is derived in the paper. The proposed solution is applied for the calculation of extreme waves during an ocean storm over a certain area. The results presented can be used as good approximation in design work of offshore installations. An extension of the proposed approach to account for nonlinearities of sea surface will be a subject of future research.
Torque Control of a Laboratory Scale Variable Speed Hydrokinetic Tidal Turbine: CFD Simulation and Validation
Authors: Ortega Arturo , Nambiar Anup , Ingram David , Sale Danny
Published: December 2020

Hydrokinetic tidal turbines are a promising alternative for the generation of clean electrical energy. They are still far behind, with respect to their technological development, in comparison to offshore wind turbines, which are currently in the stage of commercial energy production. Thus, more studies and analyses of the behaviour of tidal devices and their interaction with the surrounding ocean space are required. How this interaction is interrelated to the power production system is also necessary to be further examined. In this paper, the development of a whole system, fully-coupled model of a laboratory-scale hydrokinetic tidal turbine, along with its interactions with the ocean environment and its electrical control system is described. The model was developed in fastFlume (SOWFA, NREL) coupled with an external torque control system. The control system is developed from the optimal torque speed curve based Maximum Power Point Tracking (MPPT) algorithm. The optimal torque speed curve of the turbine used in the model was obtained from experimental work in a test tank. The hydrokinetic tidal turbine and the control system models were implemented independently. They were coupled in order to reach an energy balance between the surrounding flow, the tidal turbine, and the control system. Three flow stream velocities were imposed in the inlet of the model domain, starting the rotor from zero rotational speed. After the optimal rotational speed is attained, the electrical power generated and the loads experienced by the turbine rotor were studied. In the simulations, the tidal device is controlled to keep the optimal power production for any flow stream velocity. The results of the modelling work were compared with experimental measurements taken from 1:15th scaled testing of a fully-instrumented and controllable tidal device at the Flowave Ocean Energy Research Facility, The University of Edinburgh, a combined wave and current test facility. The results show time series of turbine and generator variables like mechanical and electrical torque and power, as well as thrust and the optimal rotational speed for each of the tested cases. The validation shows good agreement between the numerical and experimental results which encourages futures studies using the coupled model, including the turbine working in more complex flow conditions and controlled by more complex control schemes.
Study of the Efficiency and Reliability of Pressure Vessel Composite Repair
Authors: Drumond Geovana , Ribeiro Rodrigo , Pasqualino Ilson , de Souza Marcelo Igor , Perrut Valber , Lana Luiz Daniel
Published: December 2020

The degradation of equipment used in production platforms operating in a maritime environment occurs, in most cases, by corrosion defects. High to low pressure separators remain operational but suffer from a progressive reduction of wall thickness by external corrosion. Repair techniques for tubes and pressure vessels using laminate composite material are widely known and already defined by technical standards. However, there are doubts regarding the effectiveness of these repairs when performed near openings, nozzles or other stress concentrators. The objective of the present work is to verify the efficiency of the composite repair and the influence of the defect thickness. To meet these objectives, four vessels were tested until burst. The results showed that composite repair was efficient since the burst pressure of the repaired vessel was considerably higher than its limit pressure without repair.
Widening Drilling Operation: Performance Analysis on the Application of Fixed Cutter Drill Bits in Hard Rock Formation
Authors: De Moura Jeronimo , Xiao Yingjian , Ahmed Daiyah , Yang James , Butt Stephen D.
Published: December 2020

This study is an evaluation of drilling mechanisms for widening drilling operations, which are also called hole opening or enlarge drilling operations, in hard rock formations during drilling operation with fixed cutter bits. This paper focuses on correlating drilling performance, or Rate of Penetration (ROP), with drilling parameters such as Weight on Bit (WOB), rotary speed, Torque on Bit (TOB) and bit type. Laboratory Drill-Off Tests (DOT) were conducted using a drilling simulator. Natural granite specimens were penetrated using different types of fixed cutter bits with different diameters. Various magnitudes of WOB were applied during these drilling experiments in order to study drilling performance in this type of formation. A well-organized drilling experimental plan was proposed to cover both procedures of pilot holes and widening drilling operations. Comparison were made between performance conditions obtained during the drilling operations of pilot holes and similar conditions during widening drilling operations. Furthermore, bit-rock interaction was studied by comparing experimental data with that obtained from empirical models. The focus of this paper was to analyze the ROP during each stage of the widening drilling operations of a pilot hole and its correlation with other parameters. The applicability of current empirical models and their limitations in widening drilling operations in hard rock formation was analyzed. In this way, this drilling model is applied in widening drilling operations of hard rock formation with fixed cutter bits.
Theory of Nonlinear Fourier Analysis: The Construction of Quasiperiodic Fourier Series for Nonlinear Wave Motion
Authors: Osborne Alfred R.
Published: December 2020

I give a description of nonlinear water wave dynamics using a recently discovered tool of mathematical physics I call nonlinear Fourier analysis (NLFA). This method is based upon and is an application of a theorem due to Baker [1897, 1907] and Mumford [1984] in the field of algebraic geometry and from additional sources by the author [Osborne, 2010, 2018, 2019]. The theory begins with the Kadomtsev-Petviashvili (KP) equation, a two dimensional generalization of the Korteweg-deVries (KdV) equation: Here the NLFA method is derived from the complete integrability of the equation by finite gap theory or the inverse scattering transform for periodic/quasiperiodic boundary conditions. I first show, for a one-dimensional, plane wave solution, that the KP equation can be rotated to a solution of the KdV equation, where the coefficients of KdV are now functions of the rotation angle. I then show how the rotated KdV equation can be used to compute the spectral solutions of the KP equation itself. Finally, I write the spectral solutions of the KP equation as a finite gap solution in terms of Riemann theta functions. By virtue of the fact that I am able to write a theta function formulation of the KP equation, it is clear that the wave dynamics lie on tori and constitute parallel dynamics on the tori in the integrable cases and non-parallel dynamics on the tori for certain perturbed quasi-integrable cases. Therefore, we are dealing with a Kolmogorov-Arnold-Moser KAM theory for nonlinear partial differential wave equations. The nonlinear Fourier series have particular nonlinear Fourier modes, including: sine waves, Stokes waves and solitons. Indeed the theoretical formulation I have developed is a kind of exact two-dimensional “coherent wave turbulence” or “integrable wave turbulence” for the KP equation, for which the Stokes waves and solitons are the coherent structures. I discuss how NLFA provides a number of new tools that apply to a wide range of problems in offshore engineering and coastal dynamics: This includes nonlinear Fourier space and time series analysis, nonlinear Fourier wave field analysis, a nonlinear random phase approximation, the study of nonlinear coherent functions and nonlinear bi and tri spectral analysis.
Wellhead Fatigue Analysis Considering Global and Local Effects
Authors: Rezende Filipe A. , Lopes Guilherme K. , Sousa Fernando J. M. , Sousa José R. M. , Fonseca Carlos E. , Percy Joseir G.
Published: December 2020

During drilling operations, the wellhead system and top hole casings shall be designed to support dynamic loads from the connected riser through the BOP stack/LMRP. As dynamic motions are associated to stress variations, fatigue becomes a major concern for designers.

The accumulation of damage at the wellhead and close regions is dependent on several aspects, such as the riser components, the interactions soil-conductor and conductor-surface casing, and of course the environmental conditions. Consequently, fatigue analysis involves complex numerical models and requires the simulation of a huge number of loading cases.

The present paper aims to estimate the fatigue damage at critical components of the top hole casings and at the wellhead. Two different approaches were investigated. In the first, a global model is analyzed in the time domain (TD), and the Rainflow cycle counting method is used to calculate fatigue damage. The global model includes the drilling riser, wellhead, casings, and interactions between components and with soil. In the second, the same model is analyzed in the frequency domain (FD), and the Dirlik method is used to calculate fatigue damage. Additionally, to allow a better evaluation of stresses at complex geometry regions, forces and moments obtained using the TD methodology were combined with load-to-stress transfer functions, defined by means of a local model and symbolic regression (SR) analysis. The local model includes a detailed 3D model of the pressure housings, and soil-to-casing interaction.

The obtained results indicate that the pressure housings are not sensitive to fatigue, and also that the analyses performed are feasible, contributing to reduce computational costs in wellhead fatigue assessments.
Nanoparticles As Promising Additives to Improve the Drilling of Egyptian Oil and Gas Fields
Authors: Mady Ahmed , Mahmoud Omar , Dahab Abdel Sattar
Published: December 2020

Egypt is both one of the major oil-producing non-OPEC countries and one of the oldest energy producers in the Middle East. Recently, the Egyptian government have signed several agreements for the exploration of oil and gas in several provinces/regions including; the Mediterranean, the Western Desert, the Nile Delta, and the Gulf of Suez. Petroleum companies have given great attention to Egypt’s new discoveries such as Zohr Gas Field and Nour exploration prospect. Successful drilling operations to reach the oil and gas targets depends strongly on the effectiveness of the drilling fluid (mud). It can be considered as the heart of the drilling process, where they are used to fulfil several valuable functions.

Drilling fluid technology is one of the most targeted and developed technologies worldwide. Several studies have examined the use of various types of nanoparticles (NPs) to enhance the properties and improve the performance of muds. NP can be defined as a simple particle structure with a size in the range of nanometers. The effectiveness of NPs can be accredited to their small size and high surface-area-to-volume ratio. Using NPs showed promising enhancements on the rheological and filtration characteristics as well as thermal stability and carrying capacity of the drilling fluid. Moreover, adding NPs to the drilling mud was found to minimize the shale permeability and thus, promote wellbore stability. The swelling and collapse of shale formations is expected under drilling with water-based mud, which might complicate the drilling operation.

In the present work four types of NPs (nanosilica, nanoaluminium, nanotitanium, and nano copper oxide) were tested as promising additives to improve the characteristics of KCL-Polymer mud, which is mainly used to drill shaly formations. The impact of NPs-type, -size, and -concentration were thoroughly investigated using standard viscometer and API filter press. The results showed higher potential of nanotitanium and nanoaluminium to enhance the mud properties when used at small concentrations (0.3–0.5 wt.%).

This research paper discusses a latest application and presents the most valuable findings concerning the efficient use of NPs in the drilling fluid industry. On this basis, different recommendations are stated, which might help researchers to better understand NPs’ functionality in this area of application and promote using NPs-based drilling muds as cost-effective and environmental-friendly fluids to drill the Egyptian oil and gas wells.
Environmental Stress Cracking on PVDF: ISO 22088-3 (Preliminary Data)
Authors: Freitas Rafael Luis , Costa Celio , Chaves Erica , Teixeira Sylvia
Published: December 2020

This study presents the effect of bending strain upon the structure and mechanical behavior of poly(vinylidene fluoride) (PVDF). Using the ISO 22088-3 Bent Strip Method, the PVDF samples were submitted to 3.5 % and 7.0 % strain in bending for 21 days. The unstrained and strained samples were characterized by Fourier Transformed Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) and tensile tests at 23 °C.

The applied bending strain of 3.5% and 7.0 % resulted permanent deformation for both strains applied, which curvature was very close to 3.5% and 7%. The 7% strained samples showed stress-whitening, most likely due to the well-known cavitation phenomenon; while 3.5% strained samples no cavitation was seen.

Infrared spectroscopy analysis indicates a mechanically induced α to β crystalline phase transition on the outer fibers as the bending strain increases. DSC measurements showed no change on crystallinity volume fraction and melting temperature as deformation increased. The DMA showed a shift on glass transition temperature (TG) to higher temperatures and the Elastic Modulus decreased as the bending strain increased for all temperatures.

Reverse deformation had to be applied on the plastically deformed bending samples in order to straight them out to do the tensile tests. The tensile properties measured at room temperature showed the Young’s Modulus and Yield Stress decreasing as the applied bending strain increases. On the other hand, the yield strain rose as the bending strain increased.
Numerical Evaluation of Crack in Polyvinylidene Fluoride (PVDF)
Authors: Pereira Ingrid Cristina S. , da Costa Neto Celio A. , Sousa José Renato M. , Chaves Erica G. , Teixeira Sylvia
Published: December 2020

Polyvinylidene fluoride (PVDF) is an engineering thermoplastic having a high degree of sensibility to crack, which affects long-term mechanical behavior. This study evaluates the crack-sensitive of PVDF for one commercial-grade through the development of a numerical model.

Firstly, tensile tests using DIC were performed on both uncrack and pre-crack specimens to get experimental tensile as DIC-displacement, displacement-control, and load data. For pre-crack specimens, it was proposed two values of depth: 1.0 and 1.5 mm, opened by razor blade. All specimens were uniaxial tests at 23°C under 5 mm/min. Secondly, tensile tests using extensometer were implemented for uncrack samples to determine material parameters for calibration of the numerical model and comparison with DIC-displacement. Finally, a numerical model based on the FE was implemented using ANSYS-student that inputs PVDF’s material properties, which considered the elastic-plastic behavior in simulation tests.

The PVDF demonstrated significant crack sensitivity, as it can be seen in experimental and numerical data. And, the numerical model developed based on MKHP was successfully agreement against experimental data obtained by Blue Hill 3 software. Therefore, the results allowed us to observe that pre-crack acts as a stress concentration and the numerical model got well simulates this influence on the PVDF mechanical behavior.
Assessment of Global Wave Datasets for Long Term Response of Ships
Authors: de Hauteclocque Guillaume , Zhu Tingyao , Johnson Michael , Austefjord Håvard , Bitner-Gregersen Elzbieta
Published: December 2020

Ship structure design process begins with the evaluation of environmental conditions a ship is expected to withstand. This paper deals with wave data, and more specifically with global wave dataset that can be used to evaluate waves encountered by a ship along its lifetime track. Benchmark of existing global hindcast datasets is performed, having in mind its use to assess extreme ship response. The presented comparison is thus not limited to the mean and standard deviation but includes also extreme significant wave height. Wave period that can significantly modify ship behaviour is also investigated. Five different hindcast datasets are selected for the present analysis and compared with buoy and altimeter data. Area of interest is region far from the coast, and more specifically the North-Atlantic, which is currently considered the most severe for sailing ships. In such area, the global wave models are expected to provide decent results (as opposed to near shore area where a local mesh would be required). Two datasets are provided by ECMWF (ERA5 and ERA-Interim) that uses WAM model, two others are from NOaAA/NCEP and Ifremer and use WaveWatchIII, finally WAV-ERYS dataset is provided by the Copernicus program, and uses MFWAM. Some differences are observed in the wave parameters projected by different models, especially on extremes. Reasons for this scatter are briefly discussed, but more emphasis is put on the consequence for ship response. This work has been performed within IACS (International Association of Classification Societies) framework.
Umbilical Fatigue Analysis for a Wave Energy Converter
Authors: Ballard Billy , Yu Yi-Hsiang , Van Rij Jennifer , Driscoll Frederick
Published: December 2020

Unique umbilical designs for wave energy converters (WECs), including the ability to handle significantly larger motions and loads over long deployments, are often required when conventional marine umbilical designs for offshore oil and gas and offshore wind may not meet the design and cost needs of wave energy technologies. This study details a fatigue analysis of a dynamic power umbilical attached to a two-body floating point absorber WEC system, using the sea states provided for the PacWave testing facilities. The 6 degrees of freedom motion time history for the WEC was simulated, and the motions of the attachment point for the umbilical on the WEC and respective sea states were used to analyze the dynamic motions and fatigue of the connected power umbilical to predict the fatigue life. The results show that the fatigue damage observed is more significant in shallow water, and extensive fatigue damage may occur because of the larger curvature response of the umbilical. The umbilical configurations departing at 90 deg off incoming waves were found to have the highest fatigue life attributed to less extension or compression of the umbilical. However, additional bend stiffener/limiter features may need to be incorporated into the buoyancy section and touchdown regions to minimize curvature-induced fatigue.
Digital Technologies and Standardization for Next Generation of FPSO Hulls
Authors: Torres de Mattos Bernardo , de Souza Lima Figueiredo Eduardo , Queiroz Jackson Luan
Published: December 2020

New fields development deadlines are growing short every day and FPSO projects shall be adapted to sustain these new patterns, even though actual process plants are becoming larger and more complex. FPSO projects critical path is the hull construction and changes are being made to shorten the duration of this process. For this to be feasible, hull project must be standardized to fit various topside configurations and any changes made must be absorbed as quickly as possible. This requires the use of innovative solutions and digital technologies to reduce design time. The core of these solutions is the modelling of the hull digital twin during the basic design phase with a high level of structural definitions that only happen during detailed engineering phase.

This paper presents some initiatives that results in a more consistent design and on a desktop-based virtual reality model that can be used to accelerate fabrication during construction and assembly phases. Furthermore, the way of doing hull basic design is being changed.
Safety Analysis of Liquefied Natural Gas Bunkering and Simultaneous Port Operations for Passenger Ships
Authors: Iannaccone Tommaso , Jeong Byongug , Cozzani Valerio , Zhou Peilin
Published: December 2020

The use of liquefied natural gas (LNG) has been recognized as an effective alternative fuel for marine propulsion, evidently, a growing number of vessels, including passenger ships, is already running on such a fuel. While LNG bunkering can be performed in several ways, depending on transferred volumes and managerial considerations, the time spent for LNG bunkering is regarded to be a key factor to ensure the cost-effectiveness of such operation, since a minimization of bunkering duration at the berth will make port infrastructures available for more vessels. As a result, passenger embarkment is simultaneously conducted with ship bunkering, which may increase the potential risk to individuals both onboard and nearby. Given this background, this paper is to investigate the potential risk of passenger vessels with the identification of credible scenarios for port operations that can be carried out simultaneously with LNG bunkering. An approach of quantitative risk assessment is applied to determine the risk levels pertinent to proposed scenarios. For frequency analysis, the technique of the fault tree analysis is adopted to integrate the influence of human error and management policy to the likelihood of unwanted events. Consequence analysis is conducted in aids of a commercial software to simulate the impact of LNG dispersion and fires. Research findings have shown that simultaneous operations have a negative impact both on frequency and consequence of accidental scenarios arising from LNG bunkering, taking the risk beyond lower acceptance criteria. Finally, a quantification of the risk increase is proposed to help stakeholders identify criticalities and reduce the risk contributions of simultaneous operations.
Evaluation of Flow Characteristics in an Oil-Water Separator Using Computational Fluid Dynamics
Authors: Potter Terry , Acharya Tathagata
Published: December 2020

Multiphase separators on production platforms are among the first equipment through which well fluids flow. Based on functionality, multiphase separators can either be two-phase that separate oil from water, or three-phase that separate oil, natural gas, and water. Separator performances are often evaluated using mean residence time (MRT) of the hydrocarbon phase. MRT is defined as the amount of time a given phase stays inside the separator. On field, operators usually measure MRT as the ratio of active volume occupied by each phase to the phase volumetric flowrate. However, this method may involve significant errors as the oil-water interface height is obtained using level controllers and the volume occupied by each phase is calculated assuming the interface can be extrapolated from the weir back to the separator inlet. In this study, authors perform computational fluid dynamics (CFD) on a two-phase horizontal separator to evaluate MRT as a function of varying water volume flowrates (water-cut) in a mixture of water and oil. The authors use residence time distributions (RTD) to obtain MRT at each water-cut — a method that results in significantly more accurate results than the regular method used by operators. The numerical model is developed with commercial software package ANSYS Fluent. The code uses the Eulerian multiphase model along with the k-ε turbulence model. The simulation results show agreement with experiments performed by previous researchers. Additional simulations are performed to assess the effect of various separator internals on separator performance. Simulation results suggest that the model developed in this study can be used to predict performances of two-phase liquid-liquid separators with reasonable accuracy and will be useful towards their design to improve performances under various inlet flow conditions.
Seal Tight Endfitting and Means to Identify Annulus Condition for Pre-Salt Flexibles in Brazil
Authors: Brandão M. O. , Pires F. , Benirschke C. , Almeida E. , Iecker T. , Roberts A.
Published: December 2020

The development of Brazil Offshore fields using flexible pipes took the advantage of the possibility to move around lines, anticipate the production and postpone the decision of where exactly the development phase wells should be placed, making the drilling campaign easier, cheaper and faster. For the Pre-Salt fields, mainly in Santos Basin, it is observed high concentrations of H2S and CO2, two major impact contaminants for the metallic layers of the flexible pipe. A new failure mode by SCC is the most concerning one and have several approaches either focused on the installed fleet or focused in the next pipes to be delivered. SCC is a condition that induces cracks in the pipes metallic layers and need three elements to happen: water, stress and susceptible material. If one of these three elements is suppressed, the phenomena is not to happen.

This paper will cover and present a design of a seal tight end fitting also with capabilities to be seal tested from the shop during the factory acceptance test and further means to identify if the flexible pipe section is flooded or dry visually, using ROV This information is key for the integrity management of the flexible pipes applied to pre salt fields to assure the most extent of the service life.
Effect of Sinusoidal Oscillatory Flow on a Vertical Wall-Mounted Cylinder
Authors: Jang HaKun , Ozdemir Celalettin Emre , Tyagi Mayank , Liang Jun-Hong
Published: December 2020

The purpose of this study is to numerically investigate the bed shear stress and near-bed mixing due to coherent vortex structures in the vicinity of a vertically wall-mounted circular cylinder subject to an imposed finite-depth oscillatory sinusoidal flow. Previous studies reveal that the Keulegan–Carpenter (KC) number influences the formation of lee-side wake vortex structures as well as the horseshoe vortex in front of a cylinder. Therefore, parametric studies in a moderately wide range of KC from 5 to 20 are numerically performed.

In the present study, Direct Numerical Simulation (DNS) is conducted using the open-source software, OpenFOAM, that solves the three-dimensional unsteady incompressible Navier-Stokes equations using finite volume method. Nondimensional parameters used in the simulations are carefully chosen to represent the real physics. The numerical solutions are first validated using an analytical solution for the oscillating Stokes flow and the results are then systematically and quantitatively compared with the experimental measurements. The results show that the lee-side wake is significantly influenced by KC, and distinctive types of the lee-side wake are generated and classified based on KC. It is also found that both KC and the ratio of the thickness of the Stokes boundary layer to the water depth are heavily associated with the stability of the lee-side wake. In addition, the simulated size and lifespan of the horseshoe vortex agree well with the experimental data.
Analysis of the Motion Characteristics of Large Non-Metallic Composite Cages
Authors: Zhao Lin , Pan Fei , Li Qian , Jiang Zhen
Published: December 2020

A novel large reinforced HDPE cage system applied for the deep-sea aquaculture is proposed in this paper. This new structure is targeted at two main challenges facing by the deep-sea aquaculture. First, the deep-sea operation condition is much more complicated than in near shore area; second, the dynamic response and structure requirement of large-scale cages, which can be up to 80–100m in diameter and are significantly different to that of small HDPE cages. This study tackled with these two challenges by using the reinforced HDPE material and nested floating frame structure. In order to examine the integrity, safety and structure performance of this presented structure, the dynamic response of the structure subject to various working conditions are numerically simulated and analyzed in this paper. Simulation results of the new structure are compared to that of the traditional cage regarding the cage dynamic displacement, maximum strain/stress and net declination angle. The deformation results demonstrated that the maximum strain and stress on the cage collar of the new structure is much smaller than that of traditional design, and thus the new design can greatly reduce the local deformation of the cage collar and the declination angle to ensure the structure safety in severe sea conditions. The internal nested float frames can also be arranged with nets to make better use of the breeding space.
Application of Fuzzy Logic and Expert Elicitation for Quantitative Offshore Well Integrity Data Collection
Authors: Abreu Danilo Taverna Martins Pereira de , Rocha dos Santos Joaquim , Morais Carlos Henrique Bittencourt , Martins Marcelo Ramos , Colombo Danilo
Published: December 2020

The risk of uncontrolled hydrocarbon releases in oil & gas wells is mitigated through well barrier elements (such as casings, Xmas trees and packers), which are physical components capable of holding the undesired flow of reservoir fluids. Along with operational and management measures, the well barrier elements ensure the well integrity. Typically, these elements compose well barrier sets and, at least, two tested well barrier sets should be in place during the entire life cycle. Currently, limited quantitative failure data regarding well barrier elements exists, and this fact limits a migration from the qualitative approach currently in place to a quantitative one.

There are several possible sources of quantitative failure data, such as analysis of historical data, manufacturer’s data, use of commercial databases, and expert elicitation. This latter approach is based on the operational experience of experts and is adequate when there are few existing data from the other sources and limited resources (including time) to collect the data empirically.

This paper presents the application of an expert elicitation methodology for collection of well integrity failure data. This methodology is based on the application of fuzzy set theory and allows aggregating the opinions of different experts within a group in an attempt to reach consensus.

The results include a sample of the obtained data and comparison with the results from commercial databases. The collected data serves as input for reliability analysis models, which allow predicting the probability of failure/availability of well barriers along the life cycle.
A Study on the Difference in Wave Statistics Based on Storm Model for the Ship Structural Assessment
Authors: De Gracia Luis , Wang Helong , Mao Wengang , Osawa Naoki
Published: December 2020

Ocean-going vessels are under the continuous influence on the effect of the weather, e.g. wind, waves, ocean currents. Since the weather conditions are random in nature, there are situations where the shipmaster changes the ship speed or/and heading of the original sailing path to avoid harsh weather conditions according to his judgment, experience and/or using voyage optimization systems (e.g. weather routing systems). However, ship operators hardly prioritize the ship fatigue routing in their operations. It is preferable to consider the effect of different wave environment due to ship operation in the design process to make a more rational ship design of the structural members.

In this study, sailing paths are planned, adopting voyage optimization in order to reduce the probability of encountering severe sea conditions and the minimization of the fatigue accumulation in ship structures. Short-sea sequences are generated by a statistical wave storm model. The storm profiles are determined by using the cumulative frequency of short-seas which are experienced in the different voyages optimized by the algorithm. The influence of the difference in short-seas encountered by the target ship following the optimized voyages on the cumulative damage is demonstrated by a container vessel, which also considers a weather routing system in her operations. Full-scale measurement data for two years’ voyages are considered for the verification. The benefits of using voyages optimization systems focus on reducing fatigue damage to mitigate the risk of structural failure is discussed.