bluuebunny/crossref_metadata_2025 huggingface dataset:
Study on Mechanical Properties of Water Mist Acting on Plane Shock Wave
Authors: Zhao Pengduo , Wang Haojie
Published: December 2020

The fine water mist has a significant effect in dealing with fire, gas explosion and other disasters of ships and offshore platforms. In this paper, the correlation formula of water mist acting on the plane shock wave front is derived. By combining with the correlation formula of shock wave tube flow parameters, the classical theory of solving shock wave tube flow parameters is improved, so that it can be applied to the action of water mist on plane shock wave without considering the amount of evaporation. The results of shock wave pressure and wave velocity calculated by the above theoretical formula are compared with experimental data, and the errors are all within 10%, thus verifying the applicability and reliability of the above formula. On this basis, the effects of water mist mass concentration and specific internal energy of droplet after wave on shock wave pressure and shock wave velocity are studied, and different heat absorption methods are compared. The results show that the greater the mass concentration of water mist is, the stronger the weakening effect on the shock wave, indicating that the fine water mist can weaken the strength of shock wave; and specific internal energy of droplet after wave is an important parameter that affects the degree to which the water mist weakens the shock wave. In the case of a small amount of evaporation, sensible heat absorption is the main mechanism for the water mist to weaken the shock wave.
Dynamic Characteristics and Stability of Flexible Riser Under Consideration of Non-Uniform Tension and Internal Flow
Authors: Yan Dingbang , Guo Shuangxi , Li Yilun , Song Jixiang , Li Min , Chen Weimin
Published: December 2020

As oil and gas industry is developing towards deeper ocean area, the length and flexibility of ocean risers become larger, which may induce larger-amplitude displacement of flexible riser response due to lower structural stiffness against environmental and operational loads. Moreover, suffering not only the external fluid loads coming from environmental ocean wave and current, these risers also convey internal flow. In other words, the dynamic characteristics and response of the flow-conveying riser face great challenge, such as bucking, divergence and flutter, because of the fluid-solid coupling of the internal hydrodynamics and riser structural dynamics.

In this study the dynamic characteristics and stability of a flexible riser, under consideration of its internal flow and, particularly, non-uniform axial tension, are examined through our FEM numerical simulations. First, the governing equations and FEM models of a flexible riser with axially-varying tension and internal flow are developed. Then the dynamic characteristics, including the coupled frequency and modal shape, are presented, as considering the speed of internal speed changes. At last, the dynamic response and corresponding stability behaviors are discussed and compared with the cases of riser with uniform tension. Our FEM results show that the stability and response are quite different from riser with uniform tension. And, the time-spatial evolution of riser displacement exhibit a strong wave propagation phenomenon where travelling wave are observed.
Numerical Recreation of the Draupner Wave in Crossing Wave Systems Using Smoothed Particle Hydrodynamics
Authors: Kanehira Taiga , McAllister Mark L. , Draycott Samuel , Nakashima Takuji , Taniguchi Naokazu , Doi Yasuaki , Ingram David , van den Bremer Ton S. , Mutsuda Hidemi
Published: December 2020

Freak waves, abnormally large waves, that occur in the open-ocean can cause significant damage to offshore structures and vessels. In this paper, we attempt to numerically reproduce the experiments of McAllister et al., (2019, J. Fluid Mech. [1]), to investigate the potential properties of the Draupner freak wave [2] in more detail. We use a Smoothed Particle Hydrodynamics (SPH) method to solve the full-3D Navier-Stokes equations. This Lagrangian method is able to recreate wave breaking, and has the potential to fully reproduce these experiments with the aim of providing further insight into properties of the waves created such as their kinematics and geometry.

We compare time histories of water surface elevation produced numerically using four different particle sizes with experimentally-obtained data. We find good agreement in the time domain, with r2 (coefficient of determination) values between experimental and numerical data of over 0.94 the error in maximum wave height was less than 5 % for the finest particle size (over 100 million particles). We also numerically reproduce wave breaking observed in the experiments, where jet formation and breaking phenomena are qualitatively similar in appearance.
Study on the Suppression of Vortex Induced Oscillation of Cylinder by Forward Jets
Authors: Dai S. S. , Tang D. , Younis B. A. , Fu G. Q.
Published: December 2020

Oscillation induced by vortex shedding often causes fatigue damage of slender cylindrical structures in many engineering fields, so it is significant to study the suppression of vortex induced oscillation. We focus on the methods of experimental test to study on the suppression effect of vortex induced oscillation of cylinder with single freedom at Reynolds number of 2.4 × 104. We designed a set of device with forward water jet to suppress vortex induced oscillation. We found the most notable observation from a serials of experiments: reduction of displacement of cylinder exhibits two distinct modes separated by a sudden and very pronounced decrease in the extent of cross-flow displacement at a critical value of the geometric and flow variables followed by what appears to be a saturation regime where no further decrease is observed. These results will provide some meaningful and evaluable references for practical application in ocean engineering.
Improved Thermal Model for Hydrate Formation Drilling Considering Multiple Hydrate Decomposition Effects
Authors: Liao Youqiang , Sun Xiaohui , Wang Zhiyuan , Sun Baojiang
Published: December 2020

Hydrate is ice-like solid non-stoichiometric crystalline compound, which is stable at favorable low temperature and high-pressure conditions. The predominant gas component stored in naturally-occurring hydrate bearing sediment is CH4 and is estimated about 3000–20000 trillion cubic meter worldwide. Thus, it has attracted significant research interests as an energy source from both academic and industry for the past two decades.

Ensuring drilling safety is much important to realize efficient exploitation of hydrate source. Additionally, accurate prediction of wellbore temperature field is of great significance to the design of drilling fluid and cement slurry and the analysis of wellbore stability. However, the heat transfer process in wellbore and hydrate layer during drilling through hydrate formation is a complex phenomenon. The calculation method used in the conventional formation cannot be fully applied to hydrate reservoir drilling, largely due to the complex interactions between the hydrate decomposition, multiphase flow and heat transfer behaviors.

In this study, an improved thermal model of wellbore for hydrate layer drilling process is presented by coupling the dynamic decomposition of hydrate, the transportation of hydrate particles in cuttings and heat transfer behaviors in multiphase flow. The distribution of temperature field and rules of hydrate decomposition both in wellbore and hydrate layers are thoroughly analyzed with case study, which is very helpful for the designing drilling parameters, avoiding the gas kick accidents. As well as making a detailed guidance of wellbore stability analysis.

This proposed mathematical model is a more in-depth extension of the conventional temperature field prediction model of wellbore, it can present some important implications for drilling through gas–hydrate formation for practical projects.
Numerical Study of Underwater Inflatable Co-Prime Sonar Array (UICSA)
Authors: Li Yanjun , Thomas Jordan , Ouyang Bing , Su Tsung-chow , Ahmad Fauzia
Published: December 2020

Underwater Inflatable Co-Prime Sonar Array (UICSA) is a compact sonar array assembly that can be deployed in the ocean then morph into a predetermined length to work. As a sonar array, it is critical to reduce the structural deflection and maintain sensor spacing under external forces like ocean currents. The array, like the mooring system, is affected by ocean currents. In this paper, we conduct the numerical study of the morphed UICSA made of different materials in different current conditions using OrcaFlex. The results can evaluate the performance of different UICSA systems and determine the optimal UICSA design.
Retracted: “On the Role That the End Shape of an Underwater Vehicle Plays on Wave-Induced Vertical Forces” [ASME 2020 39th International Conference on Ocean, Offshore and Arctic Engineering, Volume 6B: Ocean Engineering, Virtual, Online, August 3–7, 2020, Conference Sponsors: Ocean, Offshore and Arctic Engineering Division, ISBN: 978-0-7918-8438-6, Copyright © 2020 by ASME. Paper No. OMAE2020-18400, V06BT06A048; 10 pages; doi: 10.1115/OMAE2020-18400]
Authors: ASME
Published: December 2020

This paper was removed from publication at the author’s request. January 15, 2021.

Copyright © 2021 by ASME
Dynamic Load Analysis of the Tower Structure of a Floating Wind Turbine Under Random Wind and Wave Excitation by Detuning Blade Pitch Controller Proportional Gains
Authors: Shilun Zhao
Published: December 2020

This paper carried out coupled non-linear aero-hydro-servo-elastic simulations of a semisubmersible floating wind turbine under normal and severe sea states at various wind speeds. The NREL 5MW turbine was modeled by the SIMO-RIFLEX module in SESAM with hydrodynamic gathered by the WADAM code. A taut leg mooring system with redundancy was applied to account for the relatively shallow water site in the South China Sea. By detuning KP, the proportional gain coefficient of the blade-pitch controller, the platform motions and dynamic load effects on tower structure were investigated. It was found that the reduction of KP mitigates the load effects on tower top and base connections in certain load conditions. The motion performance of the platform was improved to some extent. The generator power output, as well as the fluctuation, were analyzed. Finally, suggestion on detailed blade pitch gains tuning according to specific wind speed and sea state was given.
Real-Time Evaluation of Structural Integrity of Tubulars in Directional Wellbores
Authors: Ramba Viswanth , Selvaraju Senthil , Subbaih Senthilmurugan , Palanisamy Muthukumar , Gauba Sanjaykumar , Jandial Suresh
Published: December 2020

The actual forces acting on the drill string in directional drilling is relatively complex than vertical drilling. In this work, the different forces acting on the drill string during directional drilling are analyzed using actual drilling data. The calculation of such forces can help driller to predict downhole complications that are caused due to drill string failures. The estimation of effective tension force at the top of the drill string requires both true tension forces and buckling stability forces acting on the drill string. True tension is a function of weight component of the drill string, the forces acting on BHA due to change in cross-sectional area and bottom pressure force acting on the drill bit and the drag forces acting on the string. The buckling stability force is defined as the difference between the internal and external force acting on the drill string. The effective tension is used to calculate the hookload and normal forces acting on the drill string. The calculation of the hookload at the deadline can help the driller to compare with actual hookload and take corrective action before the complication occurs. Further, that requires the relationship between the effective tension force at the top of the drill string and the hookload measured at the deadline. Such a relationship can be established by knowing the efficiency of the rig components such as sheave, block and tackle system, hydraulic lines and weight parameter for remaining components.

Considering the unavailability of the efficiency of these components, the following model parameters are introduced: sheave efficiency, correction factor for efficiency of block and tackle system, hydraulic lines and weight parameter for the remaining components.

All the three parameters are estimated by tuning the model with actual directional drilling data.

In another aspect, the true tension is used to locate the position of neutral point by calculating the axial stress along the drill string. The proposed model is capable of predicting the hookload at the deadline, position of neutral point and normal forces acting along the drill string. The abnormal behavior of the normal forces along the drill string is used to locate the key-seating zones. Further, the model is validated with actual directional drilling data and successfully implemented in real-time monitoring platform and the model is found to be capable of predicting downhole complications such as drill string parting and improper hole cleaning. This study is expected to provide theoretical bases for understanding the stability regions of directional well.
Capturing Wake Stiffness in Wake-Induced Vibration of Tandem Cylinders
Authors: Soares Bruno , Srinil Narakorn
Published: December 2020

When a downstream circular cylinder is in the vicinity of the disturbed wake flow which is originated from the presence of an upstream cylinder, fluid-structure interactions due to vortex- and wake-induced vibrations may coexist. Their combined effects are of practical concern for offshore structures deployed in an array or proximity such as marine risers, pipelines and mooring lines. The wake flow deficit law and wake-induced drag and lift hydrodynamic forces are modelled based on the boundary layer theory, which is modified to account for the oscillation of the upstream cylinder. Unsteady drag and lift forces associated with the vortex-induced vibration (VIV) and wake-induced vibration (WIV) are represented dynamically by van der Pol-type wake oscillators. The present paper proposes a new modelling concept and framework capable of evaluating the combined WIV-VIV of tandem circular cylinders in comparison with experimental data, capturing a key feature of the wake stiffness associated with WIV. An equivalent natural frequency based on the wake stiffness mechanism behaves equivalently to the WIV frequency. Numerical studies show that the downstream cylinder may respond in a multi-frequency scenario at specific reduced velocities. The prediction model captures the wake stiffness trend similar to the experimental observation. The correlation to the wake stiffness concept allows the identification of situations for which the downstream cylinder is mainly governed by the WIV mechanism resulting in largest vibration amplitudes.
Motion Decay Simulations of a Moored Wave Energy Converter
Authors: Jiang Changqing , el Moctar Ould , Schellin Thomas E. , Paredes Guilherme Moura
Published: December 2020

Significant cost reductions are required for marine renewable energy to become competitive. Aside from the deployment of arrays, one key area that has been identified as having potential for cost reductions is the mooring system. A challenge, therefore, is to design mooring systems which can satisfy their primary role of station keeping while being affordable and durable.

This paper presents the effects of three different mooring configurations on the motion behavior of a buoy type wave energy convertor, considering nonlinear mooring-induced fluid-structure interactions, such as the associated viscous effects. To simulate motion decay, an overset mesh method that coupled a dynamic mooring model with the Navier-Stokes equations flow solver OpenFOAM was adopted. The mooring configurations comprised an all catenary system, a catenary system with buoys, and a catenary system with buoys and clump weights. The favorable agreement between the simulations and experimental measurements validated the coupled numerical approach for simulating different mooring configurations. The mooring systems influenced not only restoring force characteristics, but also total damping of the system, which demonstrated the importance of considering mooring-induced damping when investigating moored offshore structures.
A Simple and Effective Method to Predict the Generation of Black Carbon in Oilfields
Authors: Dai Guohua , Wan Yufei , Liu Chunyu , Sang Jun , Wang Wenguang , Qian Xin , Hao Ming , Liu Renwei
Published: December 2020

As an important safety discharge facility in petrochemical industry, flare is widely used in offshore and onshore oil and gas fields to relieve pressure, vent unwanted gases. This open-air combustion system oxidizes the fuel gases into carbon dioxide and water vapor and hence avoids the contamination of air with harmful gases that cause air pollution and climate change. With the increasingly strict requirements of environmental protection and the implementation of low-carbon development policy, the black carbon (soot) caused by incomplete combustion from the flare will be strictly controlled. At present, there is no simple and effective method to determine whether the flare produces visible black carbon which exacerbates the pollution. According to the investigation on site, there are different degrees of black carbon emission from the flares both in the onshore and offshore oilfield, which brings some troubles to the petroleum corporation. Based on a flare tip and the associated gas from an oilfield in Bohai Bay of China, a simulation model, which in accordance with the actual situation, was established with the Computational Fluid Dynamics software. The Non-Premixed Combustion model was used to simulate the Combustion, the P-1 model was adopted to calculate the thermal radiation and the Moss-Brookes model was selected to compute the generation of black carbon. The feasibility of the model was demonstrated by comparing the simulation results with the field test results. Then the limitation of current conventional practice to predict whether the soot is produced, was demonstrated with the model. At the same time, the production rate of black carbon under different conditions of components and fraction were calculated. After a comprehensive analysis and comparison, a simple, directly and effective method to predict the soot was proposed. When the C-to-H ratio of fuel gas is greater than 0.273, it tends to visible soot, and when the C-to-H ratio is greater than 0.285, it tends to heavy soot, which is in line with the actual in site. Therefore, the method can be applied to predict the level of the generation of black carbon in the engineering.
Hull Structural Strength Evaluation Based on Fiber Bragg Gratings Pressure Sensors to Measure Spatial Pressure Distribution on Ship’s Hull in Waves
Authors: Komoriyama Yusuke , Ota Daichi , Ma Chong , Sawada Hiroshi , Oka Masayoshi , Matsui Sadaoki , Houtani Hidetaka
Published: December 2020

In this study, the feasibility of Fiber Bragg Gratings (FBG) pressure sensors is verified for hull structural strength evaluation. To investigate the effectiveness of FBG pressure sensors for the strength evaluation, the towing tank test is carried out with a pure hydro-structural (PHS) ship model, which is capable of elastic deformation. FBG pressure sensors are installed on the outer hull surface and FBG strain sensors are installed inside the hull to calculate a vertical bending moment (VBM). Measured water pressure is interpolated on the whole hull surface by using the weighted average approach based on relative distance. Finite Element Analysis (FEA) is carried out based on interpolated water pressure. In FEA, inertia force is considered according to the inertia relief method, and VBM is calculated by FEA results. The strain measured by FBG strain sensors is transformed to VBM based on the calibration coefficient obtained by the vertical bending test. Finally, VBM obtained by the measured water pressure and strain are compared. As a result, VBM obtained by the measured water pressure is consistent with ones obtained by the measured strain. Therefore, the availability of water pressure measured by the FBG pressure sensors is validated for the hull structural strength evaluation in terms of VBM.
Transient Response of the Steel Plate to Underwater Explosion Bubble
Authors: Chen Yingyu , Yao Xiongliang , Liu Liangtao , Gan Ning , Cui Xiongwei
Published: December 2020

In this paper, a coupling eulerian langarian method (CEL) is used to study the interaction between a collapsing underwater explosion bubble and a steel plate. The VOF method is used to simulate the physical process of bubble growth, contraction and collapse, while the finite element method is used to calculate dynamic response of the steel plate. By establishing the three dimensional numerical model, the study reveals the interesting insights into the complex problem of interaction a underwater explosion bubble and a steel plate, including the physical process of bubble growth, contraction and collapse, the dynamic response of the steel plate, as well as the wall pressure induced by the bubble dynamic. The results indicate that the elastic-plastic plate will generate permanent deformation loaded by the water jet; owing to the deformation of the nearby structure, the bubble shows as a “hazel” in the bubble contraction phase and forms toroidal jet which leads the bubble into several toroidal bubbles in the bubble collapse phase. This paper aim at proposing an effective numerical method which can be useful for the problem of strong interaction between bubble and structure.
Research on the Obstacle Avoidance Strategy for the Wave Glider in the Maritime Environment Containing Dynamic Obstacles Based on the Improved Artificial Potential Field Method
Authors: Wang Daoyong , Tian Xinliang , Zhang Xiantao , Guo Xiaoxian , Wang Peng
Published: December 2020

As a wave-propelled and persistent unmanned surface vehicle, wave glider has been widely applied in marine monitoring. Due to its long voyage, the wave glider inevitably encounters various obstacles at sea, which may cause collision accidents. However, considering the characteristics of weak maneuverability and underactuation of it, the obstacle avoidance for the wave glider is challenging. In this paper, the dynamic obstacle avoidance strategy for the wave glider based on an improved artificial potential field (IAPF) is proposed. The IAPF is committed to addressing the local minimum in the traditional artificial potential field and the obstacle avoidance difficulties caused by the weak maneuverability of the wave glider. Various simulations are conducted to demonstrate the feasibility of the proposed strategy by adopting an eight-degree-of-freedom mathematical model of the wave glider. The simulation results show that the wave glider can accomplish the obstacle avoidance task with the proposed IAPF algorithm when facing with different dynamic obstacles under various marine environments.
Autonomous Surface Vessel Obstacle Avoidance Based on Hierarchical Reinforcement Learning
Authors: Zhou Chang , Wang Lei , Yu Shangyu , He Huacheng
Published: December 2020

The obstacle avoidance problem of autonomous surface vessels (ASV) has attracted the attention of the marine control research community for long years. Out of safety consideration, it is important for ASV to avoid all kinds of obstacles like shores, cliffs, floaters and other vessels. Developing a heading and path planning strategy for ASV is the main task and the remaining challenge. Traditional obstacle avoidance algorithms lead to too much computing in working environment. The issue of computation cost can be solved by training obstacle avoidance models with reinforcement learning (RL). By using the RL method, the ASV will choose the most efficient action according to the ASV’s experience it learned from the past. In this paper, RL is adopted to design a decision-making agent for obstacle avoidance. To train the obstacle avoidance model under a sparse feedback environment, hierarchical reinforcement learning (HRL) method is applied. Using this algorithm, better obstacle avoidance performance and longer survival time can be achieved. Memory pool modification and target network modification are also used to smooth the training process of the ASV. Simulation results demonstrate that HRL can make the learning process of un-manned ship’s obstacle avoidance smoother and more effective. Also, the living time of ASVs is improved.
Modeling Fluid Flow in Tight Unconventional Reservoirs: Micro/Nano Scale Approach
Authors: Qaddoura Rabab , Aldhuhoori Mohammed , Alkuwaiti Hamda , Belhaj Hadi
Published: December 2020

The need for a tool to predict transport phenomena in petroleum unconventional tight reservoirs is placing more stringent demand on establishing more realistic models beyond the currently used viscous and inertial dependent models.

Since diffusion is the principal mechanism in tight unconventional reservoirs that take place in both Micro and Nano scales, a diffusive term was added to the diffusivity model that operates both viscous and inertial forces, introduced by (Belhaj, et al., 2003).

This diffusive term is a modified Fick’s 1st Law. It counts for the flow velocity caused by the diffusion process. Using the three-term model as a rate equation, in addition to the continuity equation and the EOS, a new model (a form of PDE) has been developed.

The new model works ideally in unconventional tight reservoirs where oil and/or gas flow. The model has been numerically solved and tested. A comprehensive parametric study has been conducted and revealed clear trends. It has been concluded that diffusion mechanism contribution to flow increases with low permeability of the medium and low viscosity of the flowing fluid. An index (a combination of permeability and viscosity) has been developed and used to verify the influence and impact of the diffusion forces.
Experimental Study of Wave Loading by Internal Solitary Waves on a Submerged Slender Body
Authors: Ji Meng , Chen Ke , You Yunxiang , Zhang Ruirui
Published: December 2020

Although ocean structures are complex, they all can be disassembled into a number of simple-shaped parts. One common shape is the slender body mentioned in this paper, and we focus on studying the mechanism of this shape. Experiments were carried out to study features of wave loads exerted by internal solitary waves (ISWs) on a submerged slender body. ISWs were generated by a piston-type wave maker in a large-type density stratified two-layer fluid wave flume. Using a three-component force transducer, the force variation of three degree of freedom (DOF) on the model was recorded. A satisfactory prediction method is established for ISWs on a submerged slender body based on internal solitary wave theory, Morison equation and pressure integral. Calculations based on this new prediction method are in good agreement with the experimental results. The experimental results and calculations show that, different incident angles, wave amplitude and layer thickness ratio have great effects on the wave loads, especially transverse incident waves bring much more severely influence. Besides the forces increase linearly with the wave amplitude becoming larger, and the maximums of the horizontal forces increase with the layer thickness ratio increasing.
Comparison Between ERA5 and CFS Datasets of Extratropical Cyclones Associated With Extreme Wave Events in the Atlantic Ocean
Authors: Gramcianinov C. B. , Campos R. M. , Guedes Soares C. , de Camargo R.
Published: December 2020

Atmospheric and ocean datasets using numerical modeling allied to data assimilation are valuable tools for planning and maintaining marine activities, particularly due to their spatial coverage and resolution. However, even modern analyses and reanalyses present critical errors where cyclonic winds are often underestimated in some locations, leading to issues in wind-wave climate hindcasts and forecasts. This work aims to evaluate two of the newest datasets available regarding their ability to reproduce extratropical cyclone tracks associated with extreme waves in the Atlantic Ocean. The analysis is focused on the storm track position and cyclone intensity, two important features that control the wave climate. The datasets used are the ECMWF’s ERA5 and NCEP’s CFSv2. The cyclones are identified and compared between 2011 and 2018 using the relative vorticity at 850hPa and the intensity is measured through the 10-meters wind speed. The results show that the differences in track density exist mainly in coastal areas and they can be related to the coarser resolution of CFSv2 compared to ERA5. CFSv2 presents a higher number of cyclones associated with extreme wave events in the South and North Atlantic, corresponding to 87.1% and 89.2% of the cyclones identified, while ERA5 presents 66.6% and 59.5% respectively. The maximum intensity distribution shows that CFSv2 tends to produce more intense cyclones than ERA5, even for identical storms in the datasets. The distances of matching cyclones in the two datasets are around 0.5°.
Characterization and Modeling of Asphaltenes for Complex Reservoirs in Venezuela: State of the Art
Authors: Rodriguez M. Fernancelys
Published: December 2020

Asphaltenes are complex hydrocarbon molecules that are in suspension in the oil, stabilized by resins, which may cause severe production issues at reservoir and surface conditions. High asphaltene and resin contents is one of the main characteristics of the Venezuelan unconventional oils (highly viscous oils) in the Orinoco Oil Belt. This high concentration of resins in the oil maintains the aggregates of asphaltenes dissolved in the continue oil phase avoiding asphaltene precipitation/ flocculation/deposition issues at field conditions as some Venezuelan conventional oil reservoirs located in northern Monagas State in which unfavorable resins/asphaltene (R/A) ratios promote the precipitation of asphaltenes.

Conventional oil reservoirs in northern Monagas show gravitational segregation, this is the case of Carito-Mulata and Santa Barbara Field, varying from an upper zone of critical fluid behavior to a black oil zone in the lowest part of the structure in which the current pressure levels induce asphaltene precipitation, causing problems by plugging reservoirs, wells and pipelines, severely affecting oil and gas production. This causes increased production costs (chemical cleaning) and/or irreversible formation damage when reservoir pressures are less than asphaltene precipitation/flocculation onset pressures. Therefore it is necessary to characterize the asphaltene thermodynamic behavior and include this in reservoir numerical-simulation models, with the aim of increasing the reliability of the results and optimizing production strategies.

Reproducing the thermodynamic behavior of asphaltenes is very complex, both experimentally and in numerical simulation, especially in terms of description and measurement of the degree of asphaltene-porous media interaction and the effect of injected fluids into the reservoir (EOR methods such as miscible/non-miscible gas injection or chemical flooding). Nevertheless, efforts have been done by the Venezuelan National Oil Company and collaborators, both at laboratory and simulation scales, to study the asphaltene thermodynamic behavior and the effect of permeability reduction in the porous media and its impact on the production profiles for complex Venezuelan reservoirs.

This article presents a literature review of the Venezuelan experience for the characterization and modeling of asphaltenes for conventional and heavy oil reservoirs.
Risk Assessment and Countermeasure on Drilling and Production Process of Deep Water Gas Hydrate in the South China Sea
Authors: Yuan Zhu , Kang Liu , Guoming Chan
Published: December 2020

Deep-water natural gas hydrate has high environmental risk and high technical difficulty in drilling and production. In order to promote the development of gas hydrate, we develop the assessment methods and control technologies for the operation risk during hydrate drilling and production. The work completed includes:

(1) Safety analysis of conductor and wellhead for the hydrate drilling and production

Establish a pipe-wellhead stability model to determine the drilling and working conditions under different working conditions.

(2) Risk assessment of wellbore blockage in hydrate drilling and production

Construct a wellbore multiphase flow analysis model to determine the amount of drilling inhibitor injection; obtain the location and extent of the hydrate blockage.

(3) Risk assessment of wellbore instability in hydrate production

Combined with hydrate formation properties, ground stress distribution and casing mechanics model, the position of the formation instability, and the damage of casing crushing is determined.

(4) Gas diffusion risk assessment due to hydrate decomposition in water

Study the distribution of underwater gas diffusion formed by large-area decomposition of hydrate to get the overflow flow risk.

(5) Safety model and process risk assessment of hydrate drilling operations

Conduct hazard identification and operation safety analysis of hydrate drilling operations, determine the risk level of each operation stage, and support the drilling operation.
Design for Flexible Connector of Multi-Floating Structure
Authors: Hongtao Yuan , Gang Chen , Wei Zhang , Yan Yin , Yuhan Wang , Chao Wang
Published: December 2020

For the connector between the modules of a regular hexagonal multi-floating structure, it designed a flexible connector based on hinge joints and spin joints, which allowed part of rolling, pitching and torsion between adjacent modules to release bending moment and strain. A 221m multi-floating structure hydrodynamic calculation model was modeled in this paper. Firstly, the connector loads under the regular waves were calculated by ANSYS Aqwa. Secondly, structural model of a flexible connector was built by SolidWorks basing on the finite element theory. It analyzed structural strength of the flexible connectors under different load conditions of a series of wave direction angles by ANSYS Static Structral. Lastly, the results show that the design of the multi-floating structure connectors met the design requirements in different working conditions.
Application of Peak Distribution Method for Response Based Analysis of Mooring Lines Under Tropical Storms
Authors: Ghasemi A. , Drobyshevski Y. , Kimiaei M. , Efthymiou M.
Published: December 2020

Response based analysis (RBA) is a comprehensive approach for the prediction of extreme responses and design metocean conditions of offshore facilities. For RBA, the structural system needs to be modelled, and its behavior analyzed when subjected to large metocean datasets, usually comprising thousands of different sea states. Due to the dynamic and nonlinear behavior of mooring systems in floating structures, application of conventional time domain analysis for RBA of these systems is a computationally demanding process. Hence, investigation of faster solvers and more efficient methods for the RBA is inevitable. Peak distribution method (PDM), which has recently been introduced and used for response analysis of mooring systems under extreme design conditions, is a possible solution to reduce the computational efforts in RBA by reducing the number of simulations.

This study explores the utilization of the PDM for RBA of the mooring system of a turret-moored large FPSO subjected to tropical storms. Large variability of metocean parameters within such storms limits the applicability of intuitive judgement for the selection of governing sea states. The results are compared through both time-domain and frequency-domain simulations and a computationally efficient methodology is proposed. It provides a general robust framework of computing the extreme value distribution of the system response. The proposed methodology can be used for RBA of mooring lines tension under storm conditions comprising large number of sea states.
Numerical Study on the Performance Analysis and Vibration Characteristics of Flexible Marine Propeller
Authors: Ashok Kumar S. , Anantha Subramanian V. , Vijayakumar R.
Published: December 2020

This paper addresses the hydro-elastic performance of two composite marine propellers at operating condition and compares the results with conventional materials. The study involves three stages namely, design and development of a B series propeller, hydrodynamic and structural performance analysis in uniform flow and free vibration test both in dry and wet condition. In order to perform the hydro-elastic based fluid structure interaction (FSI), Co-Simulation method was adopted to couple Reynolds Averaged Navier-Strokes Equation (RANSE) based Computational Fluid Dynamics (CFD) solver and finite element method (FEM) solvers. The open water characteristics such as thrust coefficient (KT), torque coefficient (KQ), and open water efficiency (ηO) were analyzed as a function of advance velocity (J) of the propeller. A detailed study of the various blade materials by varying mechanical properties are presented. The results obtained show the variation of stress and deflection on the blade, along with the influence of the blade deformation on the performance of propeller. The vibration behaviour of the propellers were also analysed by Block-Lanczos method in FEM solver to obtain the natural frequencies and the mode shapes using Acoustic Fluid-Structure Coupling method for both dry and wet condition. Results showed that composite propeller have better hydro-dynamic property and lower vibration than metal propeller.
Development of Closed Formula of Wave Load Based Upon Long-Term Prediction: Heave Acceleration and Pitch Angle
Authors: Shinomoto Kyohei , Matsui Sadaoki , Sugimoto Kei , Ashida Shinsaku
Published: December 2020

In order to ensure the structural safety of a ship, the most severe sea states she is expected to encounter throughout her service life need to be given consideration. This is the reason why the maximum loads corresponding to such sea states are typically specified in classification society structural rules such as the Common Structural Rules (CSR) of the International Association of Classification Societies (IACS). The maximum loads used for the structural design of a ship can have a significant impact on not only her structural safety, but also her hull construction cost; therefore, it is very important that the loads be accurately estimated. The linear term of the maximum loads typically specified in some classification society rules is equivalent to a long-term predicted value with an exceedance probability of 10−8. Since the maximum loads specified in classification society rules such as the CSR were developed specifically for specific ship types, their effective application to other ship types may be somewhat limited.

Aim of our larger study is to develop a closed formula of long-term prediction for maximum loads. The formula has high accuracy and can be applied to any ship size and type. This paper focused on the heave acceleration and pitch angle, which are used for the calculation of internal loads and so on. A formula which takes into account such as the standard deviation of the hull response in irregular waves and the directional distribution of irregular waves was proposed. Main ship parameters such as ship length L, breadth B, draft d, block coefficient Cb, and water line area coefficient Cw were used for formulating the long-term prediction. The accuracy and effectiveness of the proposed formula were confirmed through various numerical calculations using a linear seakeeping analysis code developed by ClassNK. The calculation covers 154 ship models (77 existing ships × 2 loading conditions per ship).
Vortex-Induced Vibration of a Spherical Body With Free Surface Effects: Application to Tugboats With Low Length-to-Beam Ratio
Authors: Chizfahm A. , Joshi V. , Jaiman R. K.
Published: December 2020

Flow-structure interactions of submerged or floating bodies can lead to undesired behavior in many marine and offshore engineering applications. In this paper, we consider a complex nonlinear dynamical system of unsteady wake flow interacting with a freely moving tugboat in open water. To meet the operational demands of compact, agile, and high power ship-handling, new hull forms of tugboats are designed with low length-to-beam ratios and rounded sterns. While the hydrodynamic design with low length-to-beam ratios provides improved directional controllability, it can be challenging for tractor tugboats due to the massively separated wake flow with the vortex shedding. These wake vortices can cause large fluctuating yaw moments and possibly a strong fluid-structure coupling via synchronization or lock-in. Of particular interest, the proposed study will focus on the physical mechanism and control of flow-induced oscillations with free-surface effects via our in-house fully-coupled three-dimensional fluid-structure-free-surface interaction solver. Stabilized finite element based methods will be employed to discretize the partial differential equations that arise from the mathematical modeling of the physical phenomena considered. We will begin with a fundamental understanding of coupled dynamics of a canonical geometry of a freely vibrating sphere at free-surface. The physical insight gained will then be applied to a realistic tugboat configuration. We aim to understand the fundamentals of vortex-shedding modes and the coupled dynamics pertaining to the flow-induced vibration (FIV) response of a freely vibrating sphere (a prototypical problem for a rounded tugboat) in all three spatial directions. To predict and analyze the vortex synchronization regimes and the wake patterns, the FIV response of the sphere at a low mass ratio is investigated over a broad range of reduced velocities and Reynolds numbers. We find that the sphere begins to move along a linear trajectory with hairpin vortex-shedding mode, eventually transforming into a circular trajectory with spiral mode in its stationary state for Re ∈ [2000–6000]. We systematically examine these mode transitions and the motion trajectories in the three degrees-of-freedom for higher Reynolds number up to 15,000 which has not been studied in detail in the literature. Finally, we will look into the effect of free surface on the FIV response of the sphere piercing the free surface and will link our fundamental results with a realistic configuration of tugboat undergoing vortex-induced oscillation with free surface effects.
Retracted: “Nonlinear Integrated Simulation of Dropped Container Impact With Platform Deck” [Proceedings of the ASME 2020 39th International Conference on Ocean, Offshore and Arctic Engineering, Volume 2A: Structures, Safety, and Reliability, Virtual, Online, August 3–7, 2020, Conference Sponsors: Ocean, Offshore and Arctic Engineering Division, ISBN: 978-0-7918-8432-4, Copyright © 2020 by ASME. Paper No. OMAE2020-18581, V02AT02A012; 10 pages; doi: 10.1115/OMAE2020-18581]
Authors: ASME
Published: December 2020

This paper was removed from publication at the author’s request, August 30, 2021.

Copyright © 2021 by ASME
Direct Numerical Simulations on the Flow Normal to a Plate With Transit Shape From Circular Disk to Triangle
Authors: Wang Huaicheng , Tian Xinliang , Zhao Yakun , Li Jun , Li Xin , Lu Wenyue
Published: December 2020

This paper presents a numerical study of the flow normal to a triangular plate. A total of four plates with the same frontal area Ar and different curved edges are used. The curvature of edges is determined by the compression ratio k (k = 0.3, 0.4, 0.5, 0.8; the large value of k corresponds to the large curvature of the edges). A disk of χ = 50 (χ is the diameter-thickness aspect ratio) is used as the reference disk. The Reynolds number Re based on the characteristic length is up to 250. Four states are observed and denoted as: (I) steady and geometric symmetry state (SG); (II) steady and reflectional symmetry state (SR); (III) reflectional symmetry breaking with periodic flow (RSB); (IV) chaotic state (CS). The critical Reynolds numbers at the first two stages (Rec1, Rec2) decrease with the increasing k, indicating that flow of the plates with a larger curvature is more unstable. Therefore, we believe that the flow around a triangular plate is more stable than that around a circular disk.
Effect of Multiple Fracture Initiation on the Accuracy of Hydraulic Fracturing Simulation
Authors: Bennour Ziad , Mahmud Walid Mohamed , Ermila Mansur
Published: December 2020

Hydraulic fracturing is a stimulation technique in which the formation is fractured using high pressure exerted by a fluid. The induced fracture increases the permeability of the formation by providing conductive channels to the formation which results in improved fluids productivity.

Hydraulic fracturing is a common practice in oil and gas, particularly in the development of unconventional low porosity and low permeability reservoirs. However, as the hydraulic fracturing technique is costly, considerable preparations efforts must be made before executing the fracturing operation including simulating the intended fracture model.

A simulation model of a hydraulic fracturing assists in forecasting and controlling the intended fractures that are to be induced. Although the simulation model can be helpful, it may not exactly mimic or predict the actual initiated fractures due to the complex nature of the actual fracturing process. Thus, the simulated model and the actual fracture might differ in many ways which results in an uncertainty in the simulated fracture model.

Therefore, in order to reduce uncertainty, initial data input and assumptions made before and during the fracturing simulation need to be precise in order to obtain accurate simulation results. The growth of a single fracture is often assumed during the simulation of hydraulic fracturing which maybe incorrect as multiple fractures may initiate at the start or middle of the actual fracturing treatment and can have significant effect on the simulated fracturing results.

This paper proposes a method to minimize the difference between fracturing simulation and actual fracture treatment results by utilizing sensitivity tests to the main fracturing parameters. Thus, the initial actual fracturing results were used to detect the occurrence of multiple fractures where the latter was considered to enhance the upcoming simulation accuracy of the proposed treatments. The analysis of high net pressure data during the actual treatment indicates the possible presence of multiple fractures where history matching between actual treatment and simulation results data can give an estimate on when and how many multiple fractures were initiated during the fracturing treatment.

As a result, the data analysis showed that multiple fractures initiation had a significant effect on the fracture simulation results and the assumption of a single fracture during hydraulic fracturing should be discarded unless it is confirmed to be the case. Geological settings of the reservoir and the presence of natural fractures were also found to cause multiple fractures initiation during the treatments, and therefore, the reservoir data and description need to be determined properly before attempting the simulation of a fracturing treatment.