bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analytical Formulae for the Lateral Buckling Behaviour of Pipelines Installed With Residual Curvature
Authors: Teigen Martin , Ibrahim Malik 
Published: December 2020

Abstract
Residual curvature installation of subsea pipelines has become a popular method for lateral buckling management because of its low-cost implementation and high reliability. The method is foreseen to remain attractive due to the positive operational feedback made available to the public domain.
On the design methods, previous research has predicted the behaviour of pipelines installed with residual curvature mainly via finite element analysis (FEA). These analyses include lateral buckling, installation, reeling etc. Further to this, Teigen and Ibrahim have put an effort into quantifying design uncertainties using structural reliability analysis (SRA). Analytical approaches have also been explored, such as pipeline rolling, and other effects during pipeline installation. However, there is little published work on analytical approaches for the lateral buckling behaviour.
Therefore, this paper suggests analytical formulations for the lateral buckling behaviour of pipelines installed with residual curvature. For predicting the critical buckling force, the Palmer formulation was used as a basis. For predicting the pipeline integrity post buckling while accounting for non-linear effects and residual plasticity in the system, the formulation is derived using a combination of dimensional analysis, regression analysis and a modified Hobbs formulation. The resulting analytical formulation is calibrated to a database of finite element solutions.
The suggested approach is assessed for a configuration that applies model parameters based on the Skuld pipeline. A validation has been performed and the errors have been assessed to verify the suitability of the proposed analytical approach.
An Optimized Thrust Allocation Algorithm for Dynamic Positioning System Based on RBF Neural Network
Authors: Tang Ziying , Wang Lei , Yi Fan , He Huacheng 
Published: December 2020

Abstract
The thrust allocation of Dynamic Positioning System (DPS) equipped with multiple thrusters is usually formulated as an optimization problem. Hydrodynamic interaction effects such as thruster-thruster interaction results in thrust loss. This interaction is generally avoided by defining forbidden zones for some azimuth angles. However, it leads to a higher power consumption and stuck thrust angles. For the purpose of improving the traditional Forbidden Zone (FZ) method, this paper proposes an optimized thrust allocation algorithm based on Radial Basis Function (RBF) neural network and Sequential Quadratic Programming (SQP) algorithm, named RBF-SQP. The thrust coefficient is introduced to express the thrust loss which is then incorporated into the mathematical model to remove forbidden zones. Specifically, the RBF neural network is constructed to approximate the thrust efficiency function, and the SQP algorithm is selected to solve the nonlinear optimization problem. The training dataset of RBF neural network is obtained from the model test of thrust-thrust interaction. Numerical simulations for the dynamic positioning of a semi-submersible platform are conducted under typical operating conditions. The simulation results demonstrate that the demanded forces can be correctly distributed among available thrusters. Compared with the traditional methods, the proposed thrust allocation algorithm can achieve a lower power consumption. Moreover, the advantages of considering hydrodynamic interaction effects and utilizing a neural network for function fitting are also highlighted, indicating a practical application prospect of the optimized algorithm.
Towing Experiment of a Hydro-Structural Container Ship Model in Bow-Quartering Modulated Wave Trains
Authors: Houtani Hidetaka , Komoriyama Yusuke , Matsui Sadaoki , Oka Masayoshi , Sawada Hiroshi , Tanaka Yoshiteru , Waseda Takuji 
Published: December 2020

Abstract
We experimentally investigated the influence of the geometries of a modulated wave train on the vertical-bending and torsional moments acting on a container ship in bow-quartering sea conditions. We conducted a towing experiment with a hydro-structural container ship model in the Actual Sea Model Basin (ASMB) (80 m deep, 40 m wide, and 4.5 m deep) at the National Maritime Research Institute. The ship model is made of urethane foam and was designed to have similar vertical bending and torsional vibration mode shapes to an actual ship. A modulated wave train was generated in the ASMB by the higher-order spectral-method wave generation (HOSM-WG) method such that the maxim crest appeared at the center of the basin. The ship model was towed in the modulated wave train with a relative heading angle of 120 degrees. A series of tests was performed by varying the encounter timing of the ship model and the maximum crest of the modulated wave train. In the experiment, fiber-Bragg-grating strain gauges successfully measured whipping vibrations of the ship model due to a slamming impact. The experimental results revealed that the rear wave height Hr and the ratio of the rear and front wave heights Hr/Hf were the dominant parameters governing the maximum sagging and torsional moments of a ship in bow-quartering modulated wave trains.
Electrokinetics Application in Concrete and Well Construction
Authors: Jafariesfad Narjes , Geiker Mette Rica , Sangesland Sigbjørn , Gawel Kamila , Torsæter Malin 
Published: December 2020

Abstract
Electrically induced or coupled transport processes including electrophoresis, electroosmosis and electromigration in solutions and porous media under an external electric field have been extensively studied and employed in many disciplines.
For protection and rehabilitation of concrete structures, cathodic protection, electrochemical realkalization, and chloride extraction are extensively used. Other electrokinetic techniques are developed for the concrete industry, but have not been widely used so far, including electrokinetic treatment processes, for corrosion mitigation, recovery from sulfate attack, crack healing, and porosity and permeability reduction. These processes can improve the microstructure of the cement-based systems resulting in an improved performance in long-term and can be applied to repair failed structures.
Application of electrokinetic processes are rapidly extended in well construction due to the increased interest in techniques enabling manipulation of micro- and nanosized particles. The techniques could be beneficial in building a robust cement sheath in oil and gas wells. Additionally, electrokinetic remediation techniques can possibly be introduced for repairing damaged structures in oil and gas wells.
This review provides an overview of electrokinetic-based techniques, which has been introduced to cement-based materials, mainly reinforced concrete. The potential application of these techniques in oil well construction is discussed.
Research on Protective Performance of Protective Liquid Tank to Shock Wave Generated by Fragment
Authors: Hong Yang , Li Xiaobin , Bao Yuchen 
Published: December 2020

Abstract
In this paper, the simulation method is used to study the installation of metal plates in the liquid tank as a protective structure. The process of shock wave propagation in the liquid tank is analyzed by finite element software, and the metal plate deformation caused by shock wave is discussed. In addition, the pressure changes of different measuring points are compared when installing aluminum plate, steel plate and no protective structure in the liquid tank, and the effects of different protective structures on weakening shock wave are analyzed. Through the simulation method, the protective effects of the three basic parameters (the layer number, position and angle) of the protective structure are analyzed, and the effects of different forms of protective structures on the ability for weakening shock wave are also discussed. The results of this paper can provide references for the optimal design of liquid tank protection and its application in ship protection.
Application of Two Phase Eulerian CFD Model to Simulate High Velocity Jet Induced Scour
Authors: Tavouktsoglou Nicholas S. , Dimakopoulos Aggelos , Spearman Jeremy , Whitehouse Richard J. S. 
Published: December 2020

Abstract
Submerged water jet causing soil excavation is a typical water-soil interaction process that occurs widely in many engineering disciplines. In hydraulic engineering for instance, a typical example would be scour downstream of headcuts, culverts, or dam spillways. In port and waterway engineering, erosion of the channel bed or quay wall by the propellers of passing ships are also typical water jet/soil interaction problems. In ocean engineering, trenching by impinging high-velocity water jets has been used as an efficient method for cable and pipeline burial. At present, physical modelling and simple prediction equations have been the main practical engineering tool for evaluating scour in these situations. However, with the increasing computational power of modern computers and the development of new Computational Fluid Dynamics (CFD) solvers, scour prediction in such engineering problems has become possible.
In the present work three-dimensional (3D) numerical modelling has been applied to reproduce the capability of a pair of water jets to backfill an excavated trench. The simulations are carried out using a state-of-the-art three-dimensional Eulerian two-phase scour model based on the open source CFD software OpenFOAM. The fluid phase is resolved by solving modified Navier-Stokes equations, which take into consideration the influence of the solid phase, i.e., the soil particles.
This paper first presents a validation of the numerical model against vertical jet erosion tests from the literature and conducted at HR Wallingford. The results of the model show good agreement with the experimental tests, with the numerical model predicting the scour hole depth and extent with good accuracy. The paper then presents a validation of the model’s ability to reproduce deposition which is evaluated through a comparison with settling velocity data and empirical formulations found in literature, again with the model showing good agreement.
Finally, the model is applied to a prototype cable burial problem using a commercially available controlled flow jet excavator. The study found that the use of water jets can be effective (subject to confirmation of the time-scale required for real operations) for performing backfill operations but that the effectiveness is closely related to the type of sediment and selection of an appropriate jet discharge. As a result, in order for the water jet method to be effective for backfill, there is a requirement for a good description of the variation in sediment type along the trench and a requirement for the jet discharge to be varied as different sediment types are encountered.
Air Gap Assessment of Semi-Submersibles: Efficient Utilization of Model Test Data
Authors: Machado-Damhaug Ulla , Hanssen Finn-Christian W. , Brunborg Maren , Storheim Håkon , Haver Sverre 
Published: December 2020

Abstract
In linear air gap analysis of semi-submersibles, the surface elevation is modified by an asymmetry factor to account for the crest-to-trough asymmetry related to wave nonlinearity and the effect of nonlinear diffraction. The asymmetry factor varies with numerous conditions including the position relative to the semi-submersible, the sea state, the relative wave direction and the semi-submersible’s loading condition. Although simplified values for the asymmetry factor are suggested in rules and guidelines such as DNVGL-OTG-13, model tests should ideally be performed in order to get accurate values for each specific design. When considering nonlinear responses, model tests are generally done according to the contour line approach, where several realizations (seeds) of a few critical sea states are performed using the 3-hour maximum from each of these to fit a Gumbel distribution. We here seek to explore if the number of seeds can be optimized when considering the relative wave elevation (upwell) by using the less data-wasteful Peaks-Over-Threshold method.
Estimation of Environmental Contours Using a Block Resampling Method
Authors: Mackay Ed B. L. , Jonathan Philip 
Published: December 2020

Abstract
A new method for estimating joint distributions of environmental variables is presented. The key difference to previous methods is that the joint distribution of only storm-peak parameters is modelled, rather than fitting a model to all observations. This provides a stronger justification for the use of asymptotic extreme value models, as the data considered are approximately independent. The joint distribution of all data is recovered by resampling and rescaling storm histories, conditional on the peak values. This simplifies the analysis as much of the complex dependence structure is resampled, rather than modelled explicitly. The storm histories are defined by splitting the time series into discrete blocks, with the dividing points defined as the minimum value of a variable between adjacent maxima. Storms are characterised in terms of the peak values of each parameter within each discrete block, which need not coincide in time. The key assumption is that rescaling a measured storm history results in an equally realistic time series, provided that the change in peak values is not large. Two examples of bivariate distribution are considered: the joint distribution of significant wave height (Hs) and zero up-crossing period (Tz) and the joint distribution of Hs and wind speed. It is shown that the storm resampling method gives estimates of environmental contours that agree well with the observations and provides a rigorous method for estimating extreme values.
Experimental Study of Slam Forces on External Turrets With Different Top Angles
Authors: Ishihara Yuki , Murai Motohiko , Nakanishi So , Kato Shunji , Nakajima Yasuharu 
Published: December 2020

Abstract
The external turret is widely used for mooring FPSOs. However, external turrets can be exposed to slamming and it leads to generate FPSO’s whipping. To analyze the fatigue strength of the FPSOs, probability distributions of slam forces acting when slamming happens are necessary. In this study, we focus on slam force filtered by 10Hz low-pass filter. Then, we examined the probability distribution of peak slam forces, the effect of the top angle on slam forces, and the difference of two types (fixed and oscillator-mounted) tests. For three turret models with different top angle (180°, 160°, and 140°), two types of model tests were carried out.
To confirm the experiment’s validity and reliability, we compared these model tests with the previous study. The slam forces measured on a conical (140°) turret were consistent with the estimated curve in the previous study. The comparison of two types of tests indicated that fixed turret tests were an easy and valid way of measuring the slam forces on external turrets.
3-hour return values calculated by five methods were used to examine the characteristic of each turret. And these values were compared with 3-hour mean maxima to examine the difference between the five methods and experimental results. As a result, the use of Generalized Extreme Values and Generalized Pareto distributions is more suitable than using Rayleigh distribution in estimating return values of slam forces on external turrets.
Study on Mechanical Properties of Water Mist Acting on Plane Shock Wave
Authors: Zhao Pengduo , Wang Haojie 
Published: December 2020

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.