bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study on Dynamic Stability of Single Floating Pier Under Waves
Authors: He Yikuan , Han Bing , Ji Wenyu 
Published: October 2021

Abstract
Considering the upper structure restraint effect of the floating bridge, the diffraction effect and radiation effect of linear monochromatic waves, the dynamic response equation of floating pier is derived and the factors affecting the dynamic stability of the floating pier are analyzed in this paper. Based on the theory of potential flow, the calculation domain is divided into the interior region and the exterior region. The wave diffraction and radiation problems are solved by the matched eigenfunction expansion method (MEEM). After obtaining the wave excitation force, additional mass and radiation damping coefficient, considering the restraint effect of the upper structure of the floating bridge, the motion differential equation of the floating pier is established, and the response amplitude operator (RAOs) of the floating pier is obtained. The effects of span, mass and stiffness of upper structure, as well as the draft depth, size and net height of floating pier on dynamic stability of floating pier under wave are analyzed. The results show that the increase in the span of upper structure will significantly increase the peak RAOs of sway and heave, and the increase in stiffness is helpful to reduce the peak RAOs of sway and heave. The increase of the floating pier radius can reduce the heave RAO, and the net height on the water surface of the floating pier increases the heave and roll.
A Case Study on Consensus Building With Fisheries for Offshore Wind-Power Generation in Japan
Authors: Suda Sayaka , Kularathna A. H. T. Shyam , Tabeta Shigeru , Takagi Ken 
Published: October 2021

Abstract
Local fishery unions have a significant authority over the use of marine space in Japan. Building consensus with them on marine space use have been identified as significant barriers to development of offshore wind projects. Creating non-monetary benefits and adding value to the local fisheries is a required strategy for getting fisheries consensus for future offshore wind projects. Previous studies have proposed and evaluated several such benefit creation options. However, there still remains uncertainty of the effectiveness of such benefit creation options. This study aims to compare the local residents’ and fisheries’ preference of the benefit creation options by using questionnaire surveys and stakeholder interviews in three areas. Those valid responses have been selected for the preference analysis by using the DS-AHP multi criteria decision making model. This study shows that project location and other regional differences are significant factors of general residents’ attitudes of offshore wind projects. On the other hand, fishers, the most important stakeholders, preferred added values related to their fishing industry. Additionally, regional location and fishing method is found to have an impact on their preference.
Experimental Study on the End Effect and the Effect Due to the Difference in End Shape of the Fluid Force Acting on a Rotating Cylinder in a Uniform Flow
Authors: Suzuki Masahiro , Ikoma Tomoki , Aida Yasuhiro , Rheem Chang-Kyu 
Published: October 2021

Abstract
When investigating the characteristics of the fluid force acting on a rotating cylinder in a flow, three-dimensional effects such as edge shape and walls become a problem.
In this paper, we investigated the fluid force characteristics of the rotating cylinder, as well as the effect of the flow under the end of the cylinder and the shape of the cylinder end in the water tank experiment. There are three types of experimental conditions: No end flow condition, end flow condition, and condition with end plate. There are five disk-shaped end plates with different diameters, and the changes in fluid force are quantitatively summarized for each ratio between the diameter of the cylinder model and the end plate. By generating a flow under the end of the cylinder, the fluid force is significantly reduced compared to the no end flow condition. By attaching the end plate, the fluid force does not decrease even when a flow is generated under the end of the cylinder. The fluid force increases until the ratio DE/D of the diameter D of the cylinder model and the diameter DE of the end plate is around 3, but after that, it shows a constant value.
Ultimate Strength Envelope of a 10,000TEU Container Ship’s Global Hull Girder Subjected to Combined Vertical Bending, Horizontal Bending and Torsion
Authors: Wang Qinghu , Wang Deyu 
Published: October 2021

Abstract
To figure out the ultimate strength picture of the global hull girder of a 10,000TEU container ship subjected to combined vertical bending, horizontal bending and torsion, a simplified global hull girder of the chosen container ship is numerically modeled and a series of large deflection and elastoplastic nonlinear finite element analyses are conducted to obtain the ultimate strength envelope of the chosen container ship’s global hull girder subjected to combined vertical bending, horizontal bending and torsion. Based on the obtained numerical results, the equations that can quantify the ultimate strength envelope of the chosen container ship’s global hull girder subjected to combined loads are developed, which can be referred as one of the most important indexes to measure the safety performance of the chosen container ship under the most extreme loading conditions.
Numerical Investigation on Flow-Induced Vibrations of Circular Sections in Tandem Arrangement Varying Relative Distance
Authors: Peres Leal Aline , Vitor Reis Guilherme Paulo , Trentin Gonçalves Rodolfo , Luis Condino Fujarra André 
Published: October 2021

Abstract
The flow around a circular section has many applications in engineering, specifically in the offshore area, such as platforms, risers, pipelines, etc. These structures, which are submerged in water, are susceptible to flow-induced vibrations (FIV) and might oscillate at unwanted large amplitudes due to currents and waves. The Computational Fluid Dynamics (CFD) is a tool that allows the investigation of different parameters related to the flow and/or to the body. A CFD analysis is important in the initial design stage of riser arrangements, being a way to predict the best relative distance, since the flow around the upstream cylinder may strongly influence the downstream cylinder forces and movements responses, characteristic of wake-induced vibrations (WIV). In this context, this work carried out simulations to initiate numerical investigations about the flow around tandem arrangements and then properly identify characteristics of the fluid model that generate the results obtained in experiments. Two similar rigid circular cylinders in a tandem arrangement were analysed, in the stationary case and in the case allowed to move in two degrees of freedom (2DOF) — transverse and in-flow directions, with mass ratio m* = 10 and no structural damping, ζ = 0%. The computations were performed using OpenFOAM, a CFD open source software, in a two-dimensional flow and, numerical uncertainties studies were conducted to well define the results, presenting the value plus its uncertainty. There were variations of the tandem distances (T = 2D, 3D, 4D, 5.5D and 6D), at Reynolds number Re = 100. These two-dimensional flow simulations at low Re are important at the initial stage of a project, in order to filter the best results and save time for more advanced analysis. A single cylinder in a turbulent flow was also analysed, with m* = 2.52, varying reduced velocity. Analysis were done comparing forces coefficients and amplitudes with the literature, for both upstream and downstream cylinders. The vorticity was investigated, properly identifying vortex shedding pattern. For stationary cylinders, a critical distance of 4D was found, where the forces coefficients increase. For the 2DOF cylinders in laminar flow, the highest amplitude was 1.04D at VR = 7 for the downstream cylinder. When the cylinders are free to move, the initial tandem distance does not interfere the amplitude results of the upstream cylinder when VR &gt; 2, results also found in experiments at high Re, and, that justify the two-dimensional studies in low Reynolds as being the basis of a project.
Fusing Experimental Measurements and ROM Predicted Data for Wind Load Prediction With Extended Kalman Filter
Authors: Xing Xiuqing , Dao My Ha , Zhang Baili , Lou Jing , Tan Wei Siang , Cui Yongdong , Khoo Boo Cheong 
Published: October 2021

Abstract
Wind tunnel test, Computational Fluid Dynamics (CFD) simulation, and Proper Orthogonal Decomposition (POD) based Reduced Order Model (ROM) are used for wind load prediction on a LNG carrier in this project. In order to train the model for high accurate predictions and provide wind load prediction for vessel operations with high confidence level, extended Kalman Filter (EKF) based data assimilation model is developed to fuse the experimental data and the ROM predicted data.
Effects of sensor locations and sensor numbers on the data fusing are studied. Study results indicate that the single point data assimilation can help with sensor positioning and outlier data detection. Based on the standard errors at the sensor points, prediction accuracy with sorted multipoint data assimilation is higher than that with single point data assimilation.
Estimation of Probability of Fatigue Failure on Tubular Joints
Authors: Lokesh N. , Nallayarasu S. , Karunanithi S. 
Published: October 2021

Abstract
Fatigue is generally considered the most critical failure mode in mechanical and structural systems. Due to high-stress concentrations, welded joints represent the most common fatigue crack initiation in steel structures susceptible to fatigue. In India, especially in western offshore, there are about 300 platforms, and 50% of them have reached their design life but still operating due to existing oil and gas reserves. Fatigue prediction in offshore structures is an extremely complicated process involving many factors such as complicated geometry, material, loading, and environment. These uncertainties are modelled as random variables. The assessment of failure probabilities takes a basis to formulate a limit state function for the relevant failure mode and deterioration mechanisms. The fatigue failure assessment based on a simplified probabilistic approach using the application of reliability-based procedures such as the First Order Reliability Method (FORM) is a useful tool. In the simplified fatigue assessment method, the two-parameter Weibull distribution is used to model the long-term distribution of fatigue stresses. Reliability of tubular joint using known fatigue life is an important factor in decision making for life extension of aged platforms. The methodology adopted in this study uses the linear damage accumulation model of Palmgren-Miner, double slope S-N curve, and one-to-one transformation of the probability density functions of long-term stress range and uncertainties to obtain the probability of fatigue failure as a function of the service life from known fatigue life.
Attempt of Early Stuck Detection Using Unsupervised Deep Learning With Probability Mixture Model
Authors: Inoue Tomoya , Nakagawa Yujin , Wada Ryota , Miyoshi Keisuke , Abe Shungo , Kuroda Kouhei , Tamamura Hitoshi , Bilen Hakan 
Published: October 2021

Abstract
The early detection of a stuck pipe during drilling operations is challenging and crucial. Some of the studies on stuck detection have adopted supervised machine learning approaches with ordinal support vector machines or neural networks using datasets for “stuck” and “normal”. However, for early detection before stuck occurs, the application of ordinal supervised machine learning has several concerns, such as limited stuck data, lack of an exact “stuck sign” before it occurs, and the various mechanisms involved in pipe sticking. This study acquires surface drilling data from various wells belonging to several agencies, examines the effectiveness of multiple learning models, and discusses the possibility of the early detection of pipe sticking before it occurs. Unsupervised machine learning using data on the normal activities is a possible advanced method for early stuck detection, which is adopted in this study. In addition, as a countermeasure to another concern that even normal activities involve various operations, we apply unsupervised learning with multiple learning models.
A 2D Navier-Stokes Equations Solver Based on Generalized Harmonic Polynomial Cell Method With Non-Uniform Grid
Authors: Yu Xueying , Shao Yanlin , Fuhrman David R. 
Published: October 2021

Abstract
It is essential for a Navier-Stokes equations solver based on a projection method to be able to solve the resulting Poisson equation accurately and efficiently. In this paper, we present a new 2D Navier-Stokes equation solver based on a recently proposed fourth-order method, namely the generalized harmonic polynomial cell (GHPC) method, as the Poisson equation solver. The GHPC method is a generalization of the 2D HPC method originally developed for the Laplace equation. In the recent development of the HPC method, loss of accuracy on highly stretched or distorted grids has been reported when solving the Laplace equation, while the performance of the GHPC method on non-uniform grids is still not explored and discussed in the literature. Therefore, the local accuracy of the GHPC method is investigated in detail in the present study, which reveals that the GHPC method allows for the use of much larger grid aspect ratio than that for the original HPC method. Global accuracy of the GHPC method on stretched non-uniform girds is also thoroughly analyzed by considering cases with analytical solutions. Obvious advantages of using the GHPC method in terms of accuracy are demonstrated by comparing with a second-order central Finite Difference Method (FDM). The present Navier-Stokes equations solver uses second-order FDMs for the discretization of the diffusion and advection terms, which may be replaced by other higher-order schemes to further improve the accuracy. Meanwhile, an immersed boundary method [1] is used to study the fluid-structure-interaction problems. The Taylor-Green vortex and flow around a smooth circular cylinder are studied to confirm the accuracy and efficiency of the new 2D Navier-Stokes equation solver. The predictions show good agreements with the experimental and numerical results in the literature.
Focused Plunging Breaking Waves Impact on Cylinder Group in Deep Water
Authors: Cui Ting , Kamath Arun , Wang Weizhi , Yuan Lihao , Han Duanfeng , Bihs Hans 
Published: October 2021

Abstract
The correct estimation of wave loading on a cylinder in a cylinder group under different impact scenarios is essential to determine the structural safety of coastal and offshore structures. This scenario differs from the interaction of waves with a single cylinder but not a lot of studies focus on cylinder groups under different arrangements. In this study, the interaction between plunging breaking waves and cylinder groups in deep water is investigated using the two-phase flow model in REEF3D, an open-source computational fluid dynamics program. The Reynolds-averaged Navier-Stokes equation with the two equation k–Ω turbulence model is adopted to resolve the numerical wave tank, with free surface calculated using the level set method. In this study, focused waves in deep water were modeled with a fixed wave steepness method. Wave breaking occurs when the steepness of the wave crest front satisfies the breaking criteria. The model is validated by comparing the numerical wave forces and free surface elevation with measurements from experiments. The computational results show fairly good agreement with experimental data for both free surface elevation and wave forces. Four cases are simulated to investigate the interaction of breaking waves with a cylinder group with different relative distance, number of cylinders and arrangement. Results show that breaking wave forces on the upstream cylinder are smaller than on a single cylinder with a relative distance of one cylinder diameter. The wave forces on cylinders in the pile group are effected by the relative distance between cylinders. The staggered arrangement has a significant influence on the wave forces on the first and second cylinder. The interaction inside a cylinder group mostly happens between the neighbouring cylinders. These interactions are also effected by the relative distance and the numbers of the neighbouring cylinders.
Research on Kick Detection Model Based on Machine Learning
Authors: Song Xianzhi , Duan Shiming , Pei Zhijun , Zhu Zhaopeng 
Published: October 2021

Abstract
With the expansion of oil and gas exploration and the development of complex oil and gas resource areas, the probability of risk is increasing. Kick is one of the high-risk risks of drilling, and timely and accurate early warning is increasingly important. Based on the kick generation mechanism, kick characterization parameters are preliminarily selected. According to the characteristics of the data and previous research progress, Random Forest (RF), Support Vector Machine (SVM), Fully Connected Neural Network (FNN), and Long Short-term Memory Neural Network (LSTM) are established using experimental data from Memorial University of Newfoundland. The test results show that the accuracy of the SVM-linear model is 0.952, and the missing alarm, the false alarm rate is only 0.064, 0.035. Also, through the analysis of the kick response time, the lag time of the SVM-linear model is 3.6s, and the comprehensive equivalent time is 23.13, which shows the best performance. This paper lays a good foundation for the establishment of an intelligent kick early warning model.
Drag Coefficient for Porous Screen in a Non-Oscillating Perpendicular to Plane-in Flow
Authors: Bhandiwad M. S. , Nasar T. 
Published: October 2021

Abstract
The flow-through porous bodies/structure is one of the more advanced research in the area of energy dissipation in coastal and civil engineering fields. The experiments on the determination of drag coefficient of screens with varying porosities and for the range of flow velocities lead to explore damping ratio in a typical fluid-structure interaction problem. An experimental study has been carried out to assess the drag coefficient of the porous screens as suggested by Keulegan, G. H (1968) [3]. Six different screens with porosities of 4.4%, 6.8%, 9.2% 15%, 20% and 25% are considered. In the experiments, water with a known head from one tank is allowed to flow through a pipe equipped with porous screens into the other tank. Based on the experimental observation, the correlation between Reynolds number and drag coefficient is obtained for all porous screens. The effect of damping nature (damping ratio) of the screen for a particular range of Reynolds number has been explored. As the Reynolds number increases, the drag coefficient decreases with increasing the porosity of the screen. Further, it is understood that the value of the damping ratio decreases with an increasing relative head (H/L).
CFD Simulation of Nonlinear Deep-Water Wave Instabilities Involving Wave Breaking
Authors: Li Yuzhu , Fuhrman David R. 
Published: October 2021

Abstract
Extreme waves at the sea surface can have severe impacts on marine structures. One of the theoretical mechanisms leading to extreme waves is the instability of deep-water wave trains subject to initially small perturbations, which then grow exponentially. The present study focuses on the two-dimensional Benjamin–Feir (or modulational) instability and the three-dimensional crescent (or horseshoe) waves, also known as Class I and Class II instabilities, respectively. Numerical studies on Class I and Class II wave instabilities to date have been limited to models founded on potential flow theory, thus they could only properly investigate the process from initial growth of the perturbations to the initial breaking point. The present study conducts numerical simulations to investigate the generation and development of wave instabilities involving the wave breaking process. A CFD model solving Reynolds-averaged Navier-Stokes (RANS) equations coupled with turbulence closure in terms of the anisotropic Reynolds stress model is applied. Wave form evolutions, Fourier amplitudes, and the turbulence beneath the broken waves are investigated.
Research on Nano-Emulsion Relieving Coal Seam Water Block Damage
Authors: Sun Wei , Zhao LongHao , Wang Qian , Liu Yanchi , Zhu Weiping , Yu Guolin , Zhou Fujian 
Published: October 2021

Abstract
Hydraulic fracturing is the most effective reservoirstimulation techniques in the coalbed methane. However, the polymer in the fracturing fluid has a strong effect on the surface of the coal, causing the water lock damage as high as 70% to 90%. It is important to develop an efficient method for releasing coal seam water lock. In this paper, adsorption experiment, SEM, particle size experiment, core flow experiment, wettability and surface tension experiment are used to study the cause of coal seam water lock damage during fracturing and the effect of nano-emulsion on releasing water lock damage in coal seams. Experimental results show that after coal fracturing, the adsorption amount of polymer on the surface of coal is 14.81 mg/g. The large amount of hydrophilic polymer adsorption causes the pore radius of the coal to narrow. And the surface wettability changes from weak hydrophilic to strong hydrophilic, which increase the water lock damage. Compared with conventional slick water, fracturing fluid, the composite of nano-emulsion and fracturing fluid forms mixed micelles, which reduces the polymer adsorption capacity from 14.81 mg/g to 7.42 mg/g. After scanning by electron microscope, it is observed that the surface roughness of the rock sample is restored; The size of the nano-emulsion is about 10nm, and the very small volume can act deep in the pores of the coal seam; After using nano-emulsion, the gas/water interfacial tension is reduced by 45.1mN/m, and the wettability of coal is improved from hydrophilic to neutral, which reduces the capillary pressure in the pores of the coal and reduces the breakthrough pressure of coalbed methane by 11.1KPa; The water lock release rate is as high as 53.09%. The Nano-emulsion is an ideal choice to remove water lock damage.