bluuebunny/crossref_metadata_2025 huggingface dataset:
The Development of an Enhanced Riser Management System Including Dynamic Watch Circles for Drilling Operations in Harsh and Ultra-Deepwater Environments
Authors: Poirier Martin , Russo Massimiliano , Srikonda Rohit , Karlstad Martin , Abelsen Kjetil , Kling Curt
Published: September 2018

The operating boundaries and associated watch circles of an offshore drilling campaign are traditionally assessed by technical analysis including simulations of rig, riser and conductor/casing response to determine the mechanical limits and confirm the design limits. V a r i o u s inputs such as weather conditions, mud weights, tension settings and other critical operational aspects have to be defined in the office. The obtained results are then incorporated into a paper based Well Specific Operating Guidelines (WSOG). This traditional WSOG approach may prove particularly limiting in harsh environment and ultra-deepwater operations [1]. Traditional WSOG limits can be overly conservative, predicting excessive non-productive time and, in some cases, indicating too high risks. In some occasions these aspects may prevent planned drilling operations from being sanctioned.

In 2016, Total Exploration & Production (TEP) drilled a complex well at a record water depth of 3,404 meters in challenging environmental conditions offshore Uruguay, with up to Beaufort 10 gales, 16m maxima waves and significant ocean current often above 2 knots. These extreme conditions for the drilling campaign highlighted the necessity of an enhanced Riser Management System (RMS). This paper presents the enhanced RMS, which includes among other features, the upgrade of the BOP inclinometers with high quality sensors, soil stiffness tracking, casing monitoring, wellhead integrity and fatigue monitoring, VIV detection functionality and enhanced operability monitoring. The paper further introduces the use of Dynamic Watch Circles (DWC) and Dynamic Operability Envelopes (DOE) based on real time monitored data and actual weather conditions. Finally, the paper discusses the potential benefits of implementing an electronic WSOG (eWSOG™) replacing the traditional WSOG for extreme drilling operations.
An Inverse Problem for Parameter Estimation in a Bend Stiffener System
Authors: He Yangye , Vaz Murilo Augusto , Caire Marcelo
Published: September 2018

The top connection of the flexible pipe attached to the platform supporting structure is considered to be a critical area as it sustains the highest forces and often the maximum curvature in the riser system. Bend stiffener, a polymeric structure with conical shape, is employed to limit the maximum curvature of the riser at the uppermost connection, and protect it against excessive bending and accumulative fatigue damage. In this work, an inverse problem methodology is proposed for estimating unknown parameters in the bend stiffener system, based on a large displacement beam theoretical model combined with the Levenberg-Marquardt Method. The global mathematical formulation is used for nonlinear analysis of the riser/bend stiffener system considering linear elastic symmetric material. A case study is given considering simulated angle measurements in five monitoring positions to estimate two unknown parameters in the system, top tension and polyurethane Young’s modulus. Monte Carlo method is employed to analyze the statistic properties of the estimated parameters with measurement errors. The effects of sensor locations and measurement error ranges on the accuracy of parameter estimation are investigated. It is shown that the proposed procedure can estimate efficiently and accurately unknown parameters in a bend stiffener system. The parameter estimation procedure can also be used to assess other mechanical parameters of the bend stiffener system by angle measurements in certain monitoring positions in realistic production systems.
Semi-Empirical Single Realization and Ensemble Crest Distributions of Long-Crest Nonlinear Waves
Authors: Huang Zhenjia (Jerry) , Zhang Yu
Published: September 2018

In wave basin model test of an offshore structure, waves that represent the given sea states have to be generated, qualified and accepted for the model test. We normally accept waves in wave calibration tests if the significant wave height, spectral peak period and spectrum match the specified target values. However, for model tests where the responses depend highly on the local wave motions (wave elevation and kinematics) such as wave impact on hull, green water impact on deck and air gap tests, additional qualification checks may be required. For instance, we may need to check wave crest probability distributions to avoid unrealistic wave crest in the test. To date, acceptance criteria of wave crest distribution calibration tests of large and steep waves of three-hour duration (full scale) have not been established. Two purposes of the work presented in the paper are:

1. to define and clarify the wave crest probability distribution of single realization (PDSR) and the probability distribution of wave crest for an ensemble of realizations (PDER) of a given sea state in order to use them appropriately; and

2. to develop semi-empirical probability distributions of nonlinear waves for both PDSR and PDER for easy, practical use.

We found that in current practice ensemble and single realization distributions have the potential to be misinterpreted and misused. Clear understanding of the two kinds of distributions will help appropriate offshore design and production unit performance assessments. The semi-empirical formulas proposed in this paper were developed through regression analysis of crest distributions from a large number of sea states and realizations. Wave time series from potential flow simulations, computational fluid dynamics (CFD) simulations and model test results were used to establish the probability distributions. The nonlinear wave simulations were performed for three-hour duration assuming that they were long-crested. The sea states are assumed to be represented by JONSWAP spectrum, where a wide range of significant wave height, peak period, spectral peak parameter, and water depth were considered. Coefficients of the proposed semi-empirical probability distribution formulas, comparisons among crest distributions from numerical simulations and the semi-empirical formulas are presented in this paper.
Equilibrium Position Analysis for Offloading Operations With Turret-Moored FPSO
Authors: Huang Alex S. , Moreno Felipe M. , Tannuri Eduardo A. , Câmara Joselito G. A.
Published: September 2018

With the expansion of oil exploration in deep waters, assessing the risks associated with offloading operations becomes essential in preventing accidents that may cause huge environmental disasters.

In this paper, it will be studied the system composed of a turret-moored FPSO connected to a shuttle tanker which is assisted by a tug boat to maintain its position during an offloading operation.

Using environmental data collected over a period of 6 years, from 2004 to 2009, from the Campos Basin in Brazil, it was calculated the equilibrium positions of the system considering its constraints (vessels have to keep a minimum alignment), and verified the stability of those equilibrium points for all the given conditions.

The results obtained were simplified and grouped into operational rules using machine learning classification techniques.

Based on this static analysis, it was calculated the FPSO headings probabilities during offloading operation and the expected down time of operation in the Campos Basin.
Effect of Underlying Sand Layer on Undrained Capacity of Spudcan Foundations in Soft Clay Under Combined Loading
Authors: Wang Yifa , Cassidy Mark J. , Bienen Britta
Published: September 2018

During the operational phase, the spudcan foundations of a mobile jack-up rig are subjected to combined vertical, horizontal and moment loading. Although previous research has indicated a substantial increase in vertical bearing capacity when a spudcan penetrates through a soft clay layer towards a sand layer, the response of spudcan foundations subjected to combined loadings in such stratification has yet to be understood. This study investigates the effect of the underlying stronger sand layer on the undrained VHM capacity of a spudcan foundation using three-dimensional small-strain finite element analysis. Results show the significant increase in vertical and moment capacity, whereas the horizontal capacity is minimally affected. The soil failure mechanisms are identified and changes in the size and shape of failure envelopes, accounting for the sand layer underneath, are quantified. An analytical expression is proposed to predict the combined capacity of a spudcan foundation in clay overlying sand.
Collisions Between Ships and Platforms in Brazilian Waters
Authors: Amante Diogo do Amaral M. , Estefen Segen F.
Published: September 2018

A review of accidents involving collisions between ships and offshore platforms was carried out. There are reports and publications that present numbers, statistics and even details of the most important collisions between ships and offshore platforms, especially considering the North Sea region, but publications about accidents in Brazilian waters are rare. Thus, this paper reports the few existing publications that consider this problem in Brazilian waters and shows the results of eleven years of collecting data of collisions on Petrobras’ platforms.
Numerical and Experimental Study of SPM Fish Cage: Comparison and Validation
Authors: Cheng Hui , Huang Liuyi , Ni Yi , Xu Qingchang , Zhao Fenfang , Wang Xinxin , Liang Zhenlin
Published: September 2018

Deformations and drag forces of fish cages are two main problems in engineering design and optimization. To precisely predict these parameters, a combined numerical method, which combined the beam and truss elements, was used to study the deformation and drag forces of SPM (the single point mooring) fish cage in this paper. Flume model experiments were carried out to validate the accuracy of the numerical model. It is found that the numerical results agreed well with the experimental data, with the maximum and averaged errors of 13% and 5.9%, respectively. It can be conducted that this combined numerical model was useful in the designing and development of fish cages.
Numerical Analysis of Scale Effect on Propeller E1619
Authors: Chen Xi , Huang Yushen , Wei Peng , Zhang Zhiguo , Jin Fengfu
Published: September 2018

Simulations of propeller E1619 of two models with different scales are presented using an in-house numerical code based on the solution of the Reynolds averaged Navier-Stokes equations for the purpose of analyzing the scale effect on propellers. Propeller open water performance at given advance coefficient was obtained and compared against experimental data, showing good agreement. In aspect of CFD results, scale effect is not obvious. ITTC’78 Performance Prediction Method is applied to correct both experimental and computational open water performance of model 1. Computational KT of model 2 and corrected KT of model 1 agrees well, but the difference between computational KQ of model 2 and corrected KQ of model 1 is not neglectable. The locations of the tip vortex core of the two models are similar to each other, and so is the pressure and fluid velocity distribution. The absolute value of pressure on the blades of the smaller model is higher than the bigger model. The fluid axial velocity around the smaller model is higher than the bigger model.
Benchmark for the Sources of Uncertainty in Extreme Wave Analysis
Authors: Wada Ryota , Waseda Takuji
Published: September 2018

This paper discusses the uncertainty in extreme wave analysis from different sources. Poor data quality and small sample size will lead to uncertainty in the extreme wave analysis. Extreme value estimation methods are developed based on various assumptions, and each would lead to unique estimation results. In addition, the cause of extreme waves varies among regions, directly affecting the extreme behavior. The aim of this study is to provide insight into how the uncertainty of extreme wave estimation is influenced by the different source of uncertainty, namely data uncertainty, method selection and extreme behavior at each location.

Key parameters to describe the extreme wave events are the frequency of occurrence and its tail-behavior. We use these two parameters as a benchmark to assess the extreme wave characteristics. We focus on four regions, namely Gulf of Mexico, North Sea, Adriatic Sea, and North West Pacific. Meteorological cause of extreme events and known extreme wave behavior are reviewed based on previous studies. Model inter-comparison revealed the shortcomings of wave models to reproduce extreme wave events, and the magnitude of data error was unique to each location.

Numerical experiments were conducted to evaluate the possible impact from poor data quality and small sample size on epistemic uncertainty. Case study based on representative parameters of Gulf of Mexico and North Sea revealed the difference between two locations. These results provide a benchmark for the source of uncertainty and its impact on extreme wave analysis. Among them, extreme waves dominated by tropical cyclones were most vulnerable to have large epistemic uncertainty. The importance to adequately quantify epistemic and aleatory uncertainty is reconfirmed.
Technical Challenges for Mantle Drilling
Authors: Namba Yasuhiro , Kyo Masanori , Miyazaki Eigo
Published: September 2018

Mantle drilling, in which the oceanic crust is penetrated across the Moho to retrieve mantle samples, is one of the most challenging scientific projects of this century. This paper presents a literature survey on the development of mantle drilling, provides a brief introduction to mantle drilling, and introduces three drilling site candidates. Obstacles to mantle drilling are then presented, along with current R&D activities, plans, and considerations for solving those problems. For the purposes of this paper, significant contributions in mantle drilling research have been classified into the following categories: ultra-deep water, deep penetration, hard rocks, and high temperature. Necessary future research directions for mantle drilling are also described.
A Global-Local Damage Assessment Methodology for Impact Damage on Offshore Wind Turbine Blades During Lifting Operations
Authors: Verma Amrit Shankar , Haselbach Philipp Ulrich , Vedvik Nils Petter , Gao Zhen
Published: September 2018

Lifting the latest generation offshore wind turbines using floating crane vessels is extremely challenging. This comes with an elevated risk of blades impacting the tower or surrounding structures due to excessive crane tip motions from wave induced vessel motions. The wind turbine blades are primarily made of composite materials and thus are extremely vulnerable to impact loads causing complex damages and failure modes. One of the most critical damage type for wind turbine blades is delamination because delaminations cannot always be visually detected but can cause significant strength and stiffness reductions. An explicit structural response based approach was proposed in the previous work which is used to derive response based operational limits for single blade lifting operation using floating vessels considering probability of contact/impact and damages in the blade. An assessment of such impact induced damages on the blade was mentioned which includes modelling and predicting damages in the blade for different contact scenarios representing lifting operations in different sea states along with post impact residual strength estimation. This would require an efficient damage assessment methodology which can be utilized in practice with acceptable accuracy along with a reasonable computational cost. In this work, a simplified global-local based damage assessment methodology is presented. The paper focusses on ’shell-to-solid submodelling’ based impact damage prediction along with a brief outline of ’shell-solid coupling’ based residual strength study. The paper further presents the submodelling technique for impact investigations on DTU 10 MW blade section for a case when a projectile impacts the leading edge. Intraply damage mode based on Hashin failure criteria and Puck’s action plane theory was utilized as VUMAT in Abaqus-Explicit along with surface based cohesive behavior to model the inter-laminar failure mode. Finally, the damages and failure modes in the blade including impact induced delaminations are reported.
ADCP Observation and Numerical Model Prediction of Tidal Currents Near Kozu Island
Authors: Kodaira Tsubasa , Waseda Takuji
Published: September 2018

Izu island chain south of Tokyo, Japan has been considered as a prospective area for ocean renewable energy development because of relatively strong tidal currents, and the Kuroshio current. An Acoustic Doppler Current Profiler (ADCP) measurement near one of the islands, Kozu island, was conducted to know ocean current variability. The ADCP, Signature500, was installed 700m away from the coast and the water depth is 32m there. The observation period is for a month from January 8th, 2017. Vertical profile of the currents was recorded every 1 m at 1 minute interval. Based on the observation, the peak tidal currents were often more than 1m/s, and the maximum total speed exceeded 2m/s. The maximum flow is probably related to the Kuroshio intrusion because temperature increased abruptly. Typical vertical profile of the current follows the logarithmic law except for the near surface area. To study the spatial distribution of the current around Kozu island, a numerical model is developed based on MIT General Circulation Model (MITgcm). The model prediction of tidal sea surface variation is in a good agreement with the observation. The model underestimated the tidal currents, but the phase is in a reasonable agreement with the ADCP observation result.
Hydrodynamic Interactions of the Truncated Porous Vertical Circular Cylinder With Water Waves
Authors: Ouled Housseine Charaf , Malenica Sime , De Hauteclocque Guillaume , Chen Xiao-Bo
Published: September 2018

Wave diffraction-radiation by a porous body is investigated here. Linear potential flow theory is used and the associated Boundary Value Problem (BVP) is formulated in frequency domain within a linear porosity condition. First, a semi-analytical solution for a truncated porous circular cylinder is developed using the dedicated eigenfunction expansion method. Then the general case of wave diffraction-radiation by a porous body with an arbitrary shape is discussed and solved through Boundary Integral Equation Method (BIEM).

The main goal of these developments is to adapt the existing diffraction-radiation code (HYDROSTAR) for that type of applications. Thus the present study of the porous cylinder consists a validation work of (BIEM) numerical implementation. Excellent agreement between analytical and numerical results is observed. Porosity influence on wave exciting forces, added mass and damping is also investigated.
Combining Physics-Based and Data-Driven Models for Estimation of WOB During Ultra-Deep Ocean Drilling
Authors: Kaneko Tatsuya , Wada Ryota , Ozaki Masahiko , Inoue Tomoya
Published: September 2018

Offshore drilling with drill string over 10,000m long has many technical challenges. Among them, the challenge to control the weight on bit (WOB) between a certain range is inevitable for the integrity of drill pipes and the efficiency of the drilling operation. Since WOB cannot be monitored directly during drilling, the tension at the top of the drill string is used as an indicator of the WOB. However, WOB and the surface measured tension are known to show different features. The deviation among the two is due to the dynamic longitudinal behavior of the drill string, which becomes stronger as the drill string gets longer and more elastic. One feature of the difference is related to the occurrence of high-frequency oscillation.

We have analyzed the longitudinal behavior of drill string with lumped-mass model and captured the descriptive behavior of such phenomena. However, such physics-based models are not sufficient for real-time operation. There are many unknown parameters that need to be tuned to fit the actual operating conditions. In addition, the huge and complex drilling system will have non-linear behavior, especially near the drilling annulus. These features will only be captured in the data obtained during operation.

The proposed hybrid model is a combination of physics-based models and data-driven models. The basic idea is to utilize data-driven techniques to integrate the obtained data during operation into the physics-based model. There are many options on how far we integrate the data-driven techniques to the physics-based model. For example, we have been successful in estimating the WOB from the surface measured tension and the displacement of the drill string top with only recurrent neural networks (RNNs), provided we have enough data of WOB. Lack of WOB measurement cannot be avoided, so the amount of data needs to be increased by utilizing results from physics-based numerical models. The aim of the research is to find a good combination of the two models. In this paper, we will discuss several hybrid model configurations and its performance.
Nonlinear Effects of Wave Heights on Coupled Sloshing and Seakeeping Responses
Authors: Wang Xin , Arai Makoto , Karuka Gustavo
Published: September 2018

With increased activities in natural gas transportation and offshore exploration in the past decades, assessment of sloshing in liquefied natural gas (LNG) tanks has become an important practical issue. In this paper, we focus on the deterministic calculation of the coupled sloshing and ship motions in regular wave conditions. An in-house numerical code is used to solve the seakeeping problem coupled with the sloshing dynamics. The numerical method adopts a weakly nonlinear approach using impulse response functions for the seakeeping problem. Nonlinear Froude-Krylov and hydrostatic forces are directly evaluated in the time domain. A three-dimensional finite difference method is applied to solve the sloshing problem. The numerical method is validated by comparing with experimental results in the literature. The developed numerical method is used to analyze the nonlinear effects of wave heights.
Study of Hydrodynamic Forces on Complex Structures
Authors: Bjørke Ann-Sofie , Christensen Erik Damgaard , Carstensen Stefan , Petersen Kasper Pagh , Mandviwalla Xerxes , Kristiansen Trygve , Baarholm Rolf
Published: September 2018

This paper presents a study on the interaction of structural members that can be related to a complex structure placed in a moonpool. The complex structure in the moonpool was simplified with a varying number of members. The study has been carried out as a two-dimensional numerical study with supporting physical experiments. The focus was on the forces on the individual members as well as the entire structure. Additional the flow field associated with the oscillating water column in the moonpool was also studied.
A Strain Energy-Based Equivalent Layer Method for the Prediction of Critical Collapse Pressure of Flexible Risers
Authors: Li Xiao , Jiang Xiaoli , Hopman Hans
Published: September 2018

Flexible risers are one kind of flexible pipes that transport fluid between subsea facilities and topside structures. This pipe-like structure consists of multiple layers and its innermost carcass layer is designed for external hydrostatic pressure resistance. For the flexible risers used in ultra-deep water fields, the critical collapse pressure of the carcass layers is one of the dominant factors in their safety design. However, the complexity of the interlocked carcass design introduces significant difficulties and constraints into the engineering analysis. To facilitate the anti-collapse analysis, equivalent layer methods are demanded to help construct an equivalent pipe that performs a similar collapse behavior of the carcass. This paper proposes a strain energy based equivalent layer method which trying to bridge the equivalence between those two structures by considering equivalent geometric and material properties for the equivalent layer. Those properties are determined through strain energy equivalence and membrane stiffness equivalence. The strain energy of the carcass is obtained through numerical models and is then used in a derived equation set to calculate the equivalent properties for the equivalent layer. After all the equivalent properties have been determined, an equivalent layer FE model is built and used to predict the critical pressure of the carcass. The prediction result is compared to that of the full 3D carcass model as well as the equivalent models that built based on other existing equivalent methods, which shows that the proposed equivalent layer method gives a better performance on predicting the critical pressure of the carcass.
Ultimate Strength of Typical Stiffened Panels in Container Ships Under Random Non-Uniform Corrosion
Authors: Cui Jinju , Wang Deyu
Published: September 2018

In ship’s life cycles, corrosion can be an important factor for degradation of structural capacity. According to practical observations, non-uniform corrosion takes place instead of uniform corrosion, while investigations status quo on non-uniform corrosion are not enough and are mainly focused on unstiffened plates. So it is necessary to further study the load capacity of ship structures under non-uniform corrosion. In this paper, the ultimate strength of typical bottom panels in container ships under random non-uniform corrosion is studied by Nonlinear Finite Element Analysis (NFEA), and the load-displacement curves and collapse modes are derived. Additionally, the random nature of non-uniform corrosion is modelled and Monte Carlo Simulations (MCS) are performed to study the probabilistic characteristics of ultimate strengths for corroded structures, and the results are compared with uniform corrosion and pitting corrosion according to our previous research. Influences of boundary conditions are also studied.
Use of Clement’s ODEs for the Speedup of Computation of the Green Function and its Derivatives for Floating or Submerged Bodies in Deep Water
Authors: Xie Chunmei , Babarit Aurélien , Rongère François , Clément Alain H.
Published: September 2018

A new acceleration technique for the computation of first order hydrodynamic coefficients for floating bodies in frequency domain and in deep water is proposed. It is based on the classical boundary element method (BEM) which requires solving a boundary integral equation for distributions of sources and/or dipoles and evaluating integrals of Kelvin’s Green function and its derivatives over panels. The Kelvin’s Green function includes two Rankine sources and a wave term. In present study, for the two Rankine sources, analytical integrations of strongly singular kernels are adopted for the linear density distributions. It is shown that these analytical integrations are more accurate and faster than numerical integrations. The wave term is obtained by solving Clément’s ordinary differential equations (ODEs) [1] and an adaptive numerical quadrature is performed for integrations over the panels. It is shown here that the computational time of the wave term by solving the ODEs is greatly reduced compared to the classical integration method [7].
Penetration of Ship Anchors and the Influence of Submarine Cables
Authors: Grabe Jürgen , Heins Evelyn
Published: September 2018

Impacts by ship anchors are one of the main reasons for damage to submarine cables. Regulations meet this risk by defining a minimum permanent burial depth of submarine cables. The key parameters for the risk evaluation are the burial depth of the cable as well as the penetration depth of the anchor. In order to meet this risk sufficiently and to reduce the risk of submarine cable damage, the penetration process into the sea bed of the ship anchor has to be understood. Numerical simulations of the anchor penetration in sand are performed, in order to investigate the influence of anchor movement on submarine cables and to identify possible damage mechanisms.
Numerical Analysis of Second-Order Mean Wave Forces by a Stabilized Higher Order Boundary Element Method
Authors: Shao Yan-Lin
Published: September 2018

A stabilized Higher-Order Boundary Element Method (HOBEM) based on cubic shape functions is presented to solve the linear wave-structure interaction with the presence of steady or slowly varying velocities. The m-terms which involves second derivatives of local steady flow are difficult to calculate accurately on structure surfaces with high curvatures. They are also not integrable at the sharp corners. A formulation of the Boundary Value Problem (BVP) in a body-fixed coordinate system is thus adopted, which avoids the calculation of the m-terms. The use of body-fixed coordinate system also avoid the inconsistency in the traditional perturbation method when 2nd order slowly-vary motions are larger than the linear motions.

The stabilized numerical method presented in this paper is based on streamline integration and biased differencing scheme along the streamlines. The presence of convective terms in the kinematic and dynamic free surface conditions will lead to instable solution if the explicit method is used. Thus a fully implicit scheme is used in this paper for the time integration of kinematic and dynamic free surface conditions. In an implicit scheme, solution of an additional matrix equation is normally required due to the fact that the presence of convective terms are approximated using the variables at current time step rather than the previous time steps only. A method that avoids solving such matrix equation is presented in this paper, which will reduce the computational efforts in the implicit method. The methodology is applicable on unstructured meshes. It can also be used in general second order wave-structure interaction analysis with presence of steady or slowly-varying velocities.
An Evaluation of Submarine Collisions to a TLP
Authors: Storheim Martin , Dørum Cato
Published: September 2018

An engineering study was performed in 2017 to develop a multi-span suspension bridge on floating foundations across the Bjørnafjorden in Norway. The bridge was approximately five kilometers long and consisted of three main suspension spans supported by four pylons (towers). Two of the pylons were supported on tension-leg platforms (TLP) due to large water depths. The bridge has to be resistant towards collisions from passing ships. However, submarine impacts to the submerged parts of the bridge were also a challenge due to the bridge location being close to an active submarine training field.

This paper focus on the response of one such TLP towards collisions from submarines transiting below the bridge. Nonlinear explicit finite element analysis is used to study the possible collision scenarios, and the response of the TLP and the resulting bridge motion is evaluated. Further, transient failure of a tether was investigated to assess possible consequences of rupture of one of the tethers.
Numerical Simulations of Ship Bow and Shoulder Wave Breaking in Different Advancing Speeds
Authors: Ren Zhen , Wang Jianhua , Wan Decheng
Published: September 2018

The KCS model is employed for the numerical simulations to investigate the wave breaking phenomena of the bow and shoulder wave. RANS approach coupled with high resolution VOF technique is used to resolve the free surface. In order to study the speed effects on the phenomena of ship wave breaking, four different speeds, i.e. Fr = 0.26, 0.30, 0.32, 0.35, are investigated in calm water. Predicted resistance and wave patterns under Fr = 0.26 are validated with the available experiment data, and good agreement is achieved. For the Fr = 0.26 case, the wave pattern is steady, and the alternate variation of vorticity appear near the free surface is associated with the wake field. The breaking wave phenomena can be observed when the Froude number is over 0.32 and the Fr = 0.35 case shows most violent breaking bow wave. For the Fr = 0.35 case, the process of overturning and breaking of bow wave is observed clearly, and at the tail of bow wave, some breaking features of free surface are also captured. The reconnection of the initial plunger with the free surface results in a pair of counter-rotating vortex that is responsible for the second plunger and scar.
Use of Integrated Production Modeling to Estimate the Influence of Subsea Manifolds in Reservoir Production Management
Authors: Victorino Igor Ricardo de Souza , Hohendorff Filho João Carlos von , de Castro Marcelo Souza , Schiozer Denis José
Published: September 2018

Integrated analysis of reservoir and production system models for field development can improve production forecasts. This integration allows the evaluation and optimization of parameters of both systems for both financial return and accurate production prediction. This work evaluates the presence and position of manifolds and their influence on production. We use a Brazilian benchmark case to perform an integrated analysis of oilfield production evaluating the influence of various aspects of manifold systems to increase financial return. The results showed that integrated analysis of optimized manifold locations and the number of connected wells improved financial return. Thus, we recommend the inclusion of this integrated production modeling in field management.
Plain Interpretation of Freak Waves Phenomenon
Authors: Chalikov Dmitry , Babanin Alexander V.
Published: September 2018

An extremely large (‘freak’) wave is a typical though quite a rare phenomenon observed in the sea. Special theories (for example, the modulational instability theory) were developed to explain the mechanics and appearance of freak waves as a result of nonlinear wave-wave interactions. This paper demonstrates that freak wave appearance can be also explained by superposition of linear modes with a realistic spectrum. The integral probability of trough-to-crest waves is calculated by two methods: the first one is based on the results of a numerical simulation of wave field evolution, performed with one-dimensional and two-dimensional nonlinear models. The second method is based on the calculation of the same probability over ensembles of wave fields, constructed as a superposition of linear waves with random phases and a spectrum similar to that used in nonlinear simulations. It is shown that the integral probabilities for nonlinear and linear cases are of the same order of values. One-dimensional model was used for performing thousands of exact short-term simulations of evolution of two superposed wave trains with different steepness and wavenumbers to investigate the effect of wave crests merging. The nonlinear sharpening of merging crests is demonstrated. It is suggested that such effect may be responsible for appearance of typical sharp crests of surface waves, as well as for the wave breaking.
Parametric Model of Dead Leg Steady-State Thermal Performance
Authors: Sanchis Arnaud , Andersson Sonny , Jensen Atle
Published: September 2018

During thermal design of Subsea Production Systems (SPS), Computational Fluid Dynamics (CFD) is used to calculate production fluid temperatures in dead legs of the system. One purpose of such simulations could be to calculate the amount of insulation needed to avoid low temperatures in the piping system. A novel approach to this type of analysis is presented here to build a parametric model able to map the dead leg performance against any set of input parameters. The workflow relies on a response surface analysis performed from the results of a limited set of CFD simulations run on a sparse simulation matrix that covers the design space. Once generated, the parametric model provides real-time results and may be used for screening, optimization or condition monitoring purposes.
Slewing Effect of Twin Vertical Axis Turbines Supported by a Floating Platform Able to Rotate Around a Single Mooring System
Authors: Kusanagi Kazuma , Srinivasamurthy Sharath , Nihei Yasunori
Published: September 2018

In this study, we propose a new and innovative solution for harnessing offshore wind using vertical axis wind turbines (VAWT). The new type of FOWT is termed as Twin connection VAWT which uses single point mooring system consisting of two turbines capable of aligning itself against any wind direction. New-type vertical axis wind turbines are designed and developed by some of the present authors which are supported by separate floaters. The conceptual development and working mechanism of the proposed Twin connection VAWT is described in this paper based on experimental results. The yawing motion of proposed system about the moored point aligning itself to the direction of wind is confirmed in a series of dedicated experiments under only-wind condition. After aligning itself and turbines facing the direction of the wind, slow varying slewing motion phenomenon is observed during experiments. The wind forces acting on two VAWTs is examined in x-y plane and it is predicted that the forces acting perpendicular to the wind direction explains the slewing phenomenon. A physics model is conceptualized and developed to understand the yawing mechanism of the new system. A numerical simulation code is also developed to understand the yaw motion around the moored point using the steering motion equations. It is confirmed how the new system proposed can be utilized for generating clean energy.
On the Tuning-Free Statistical Model of Ocean Surface Waves
Authors: Zakharov Vladimir , Resio Donald , Pushkarev Andrei
Published: September 2018

Absence of mathematically justified criteria during development of the wind energy input and wave breaking energy dissipation source terms in Hasselmann equation (HE), used as the framework of modern operational wave forecasting models, lead to creation of plethora of parameterizations, having enormous scatter, disconnected from the physical background and obeying dozens of tuning parameters to adjust the HE model to the specific situation. We show that it’s possible, based on analytical analysis and experimental observation data, to create the new set of source terms, reproducing experimental observations with minimal number of tuning parameters. We also numerically analyze six historically developed and new wind input source terms for their ability to hold specific invariants, related to HE self-similar nature. The degree of preservation of those invariants could be used as their selection tool. We hope that this research is the step toward the creation of physically justified tuning-free operational models.
Design Under Arctic Conditions: A Summary of the Arctic Materials Project Guideline
Authors: Horn Agnes Marie , Østby Erling , Akselsen Odd , Hauge Mons
Published: September 2018

The main goal of the 10 years Arctic Materials KMB project run by SINTEF (2008–2017) and supported by the industry is to establish criteria and solutions for safe and cost-effective application of materials for hydrocarbon exploration and production in arctic regions. The objective of the arctic materials project guideline (PG) is to assist designers to ensure safe and robust, yet cost-effective, design of offshore structures and structural elements in arctic areas through adequate material testing and requirements to material toughness. It is well known that when the temperature decreases, steel becomes more brittle. To prevent brittle fracture in the Arctic, the structure needs adequate toughness for the loading seen at low temperatures. None of the common offshore design codes today consistently address low temperature applications. In this respect, arctic areas are defined as minimum design temperatures below what current international standards have considered per today, i.e. −10 °C to −14°C. For practical applications, the PG defines arctic areas as minimum design temperature lower than −10 °C.

It is acknowledging that design standards to a certain degree are based on operational and qualitative experiences gained by the offshore industry since the 1970’s. However, for arctic offshore facilities, limited operational experiences are gained by the industry. The basis of the guideline is that safe and robust design of structures and structural elements are ensured by combining standard industry practice today with learnings and findings from the 10 years Arctic Materials project.

This paper is concerned with the rationale behind the material and test requirements provided in the arctic material guideline. The material requirements will be discussed in detail with emphasis on toughness requirement, constraint effect, thickness effect, acceptance criteria and material qualification criteria.
Field Study on the Effects of Impact Frequency on the Axial and Lateral Capacity of Driven Pipe Piles in Sand
Authors: Anusic Ivana , Lehane Barry M. , Eiksund Gudmund R. , Liingaard Morten A.
Published: September 2018

With pile installation being an important part of the total project cost, improving the efficiency of the offshore operations would require resolving the uncertainties in how different installation methods influence pile capacity. This paper describes a programme of testing involving static loading tests on eight 165 mm diameter open-ended steel tubes driven into medium dense siliceous sand at a well-characterized test site in Perth, Western Australia. Six piles were installed by impact driving under two different driving frequencies, and two piles were installed by vibration with the aim of identifying the effects of impact frequency on the response of driven piles to static axial and lateral loading. It was found that the tension capacity of piles measured 1 week after installation was not significantly dependent on the impact frequency and that these piles had approximately the same capacity as the piles installed by vibration. First time load tests performed 4 months after the initial tests indicated that all pile types had a similar set-up characteristic. Inspection of static tests on lateral behavior of vibrated and impact driven piles suggests that installation method has no impact on the lateral capacity.
Quantifying the Uncertainty of the Crabbing Capability
Authors: Ferrari V. , Kisjes A. , Quadvlieg F. H. H. A.
Published: September 2018

Crabbing is a critical manoeuvre that requires all of the ship’s propulsors to counteract environmental forces. It is a complex hydrodynamic scenario in which it is difficult to assess the factors, nonetheless the crabbing capability is often calculated by means of simple static calculations which consider only means values. The ship designer or master should instead be aware of how much the crabbing capability can change when the propulsors are less efficient than expected or the wind loads are higher.

The present paper details the application of sensitivity and uncertainty methods to the crabbing manoeuvre of a ship. The objective is to estimate the sensitivity of the main parameters involved in a crabbing calculation and express the results in terms of uncertainty range. To this purpose, first a sensitivity analysis is performed, showing how the maximum sustainable wind speed of a test-case ship varies. The curves derived from this analysis are then used to estimate numerically the relation between wind speed and a variation in each parameter. Typical values of uncertainty of these parameters are presented, and finally the crabbing capability calculated taking into account the uncertainties.
Solving 2-D Slamming Problems by the MPS Method With Source Term Correction
Authors: Zha Ruosi , Peng Heather , Qiu Wei
Published: September 2018

An improved moving particle semi-implicit (MPS) method was developed to solve water entry problems. The traditional mixed source term was modified based on a prediction-correction scheme to suppress pressure oscillations. An improved free surface identification method was implemented for fluid computations. A weak coupling method was adopted for fluid-structure interaction. The structures were modeled by isotropic linear elastic particles. The application of the source term correction method leads to a better pressure prediction and therefore a more accurate interaction between the fluid and the structure. Validation studies were carried out for water entry of two rigid wedges, a rigid ship section, and a flexible wedge. The results by the present MPS method are in good agreement with experimental data and other published numerical results.
Effects of Aspect Ratio on the Hydrodynamic Performance of Circular Cambered Otter Board
Authors: Huang Liuyi , Li Yuyan , Xu Jiqiang , Xu Qingchang , Zhao Fenfang , Wang Xinxin , Tang Yanli , Jia Mingxiu , Liang Zhenlin
Published: September 2018

An otter board is an important device that provides a desired horizontal opening of a trawl net. A high lift coefficient or lift-to-drag ratio is required for an otter board to maintain fishing efficiency. In the present work, the hydrodynamic performance of a circular cambered otter board was studied by numerical simulation, including the effects of aspect ratios (AR), and flow distribution around the otter board. Model tests were conducted in the flume tank as well as a comparison to the numerical results. It showed that simulation results exhibited very good agreement with experiment results. Results demonstrated that the model otter board had a critical angle of attack (AOA) of 50° (when the stall appeared). The maximum lift coefficient and lift-to-drag ratio of the model otter board were 2.421 and 3.719, respectively. However, the maximum values of the full-scale otter board increased first and then decreased with an increasing AR. And the full-scale otter board had a better performance when AR = 2.489, it can enhance the lift coefficient by 17.4% compared with the initial otter board (AR = 1.25). In addition, the flow distribution around the otter board showed that the flow was smooth at small AOAs, when it attacked at large AOA (exceeded 55°), flow separation and eddies were appeared at the lee-side of the otter board.
CUDA Based Parallel Computation for Gauss Elimination Method
Authors: Liu Xiao , Xu Lei
Published: September 2018

The Central Processing Unit (CPU) parallel algorithm based on Computing Unified Device Architecture (CUDA) has shown great power of computing speedup ability. What performance will the new technique show in the field of structural computation? We choose the Gauss elimination method as the research object. In this study, the parallel Gauss elimination is realized in CUDA on GPU. Furthermore, we carry out two groups of numerical experiments. The first group investigates the effect of Matrix Bandwidths (MBs) and Node Numbers (NNs) on speedup ratio. The second one compares our method with the commercial software by analyzing two actual structural problems in ocean engineering.
Study on Vertical Bearing Capacity of the Riser Composite Pile in Clay
Authors: Chao Liang , Run Liu , Jun Wan , Pei Guan , Xiangyun Li
Published: September 2018

In order to meet the development need of small-scale marginal oilfield, it is proposed to use the riser and surface casing to bear the loads replacing or partially replacing the steel pipe pile foundation. In this paper, the vertical bearing behavior of variable cross-section composite pile with the diameter of upper part larger than that of lower part (composed of riser and surface casing) is analyzed by finite element method. Then, the influences of different length combinations and diameter combinations of the composite pile on vertical bearing mechanism are studied, and the characteristics of stress concentration at the variable cross-section are revealed. The calculation results show that the increase in pile diameter, pile length and diameter ratio can effectively improve the bearing capacity of riser composite piles. The vertical ultimate bearing capacity of riser composite piles is greatly affected by upper part and less affected by lower part. The bearing capacity of lower part is gradually exerted, as the plastic zone appears at the end of the upper part, meanwhile, the Q-s curve shows as a broken line, which means that a larger pile top settlement is needed in order to effectively activate the bearing capacity of lower part.