bluuebunny/crossref_metadata_2025 huggingface dataset:
Computation of Wave Added Resistance by Control Surface Integration
Authors: Pan Zhiyuan , Vada Torgeir , Han Kaijia
Published: October 2016

A time domain Rankine source solver is extended to compute the wave added resistance of ships. The proposed approach applies the momentum conservation principle on the near field fluid volume enclosed by the wet surface of a floating body, the free surface and a control surface. The wave added resistance is then calculated by the integration over the control surface of the fluid velocities and free surface elevations. To be able to incorporate the proposed method with the Rankine source code, an interpolation scheme has been developed to compute the kinematics for the off-body points close to (or on) the free surface. Two Wigley ship models, a containership model S175 and a tanker model KVLCC2 are used to validate the present method. In general good agreement is found comparing with the model test data. The convergence behavior is examined for the proposed method including the selection of the time step and location of the control surface. Both Neumann-Kelvin and double body linearization methods are evaluated with the proposed method. It is found that the Neumann-Kelvin linearization can only be applied for slender ship hull, whereas double body method fits also for blunt ships. It is suggested to apply the proposed method with double body linearization to evaluate the wave added resistance of ships with a control surface close to the ship hull.
Non-Stationary Estimation of Joint Design Criteria With a Multivariate Conditional Extremes Approach
Authors: Raghupathi Laks , Randell David , Ewans Kevin , Jonathan Philip
Published: October 2016

Understanding the interaction of ocean environments with fixed and floating structures is critical to the design of offshore and coastal facilities. Structural response to environmental loading is typically the combined effect of multiple environmental parameters over a period of time. Knowledge of the tails of marginal and joint distributions of these parameters (e.g. storm peak significant wave height and associated current) as a function of covariates (e.g. dominant wave and current directions) is central to the estimation of extreme structural response, and hence of structural reliability and safety. In this paper, we present a framework for the joint estimation of multivariate extremal dependencies with multi-dimensional covariates. We demonstrate proof of principle with a synthetic bi-variate example with two covariates quantified by rigorous uncertainty analysis. We further substantiate it using two practical applications (associated current given significant wave height for northern North Sea and joint current profile for offshore Brazil locations). Further applications include the estimation of associated criteria for response-based design (e.g., TP given HS), extreme current profiles with depth for mooring and riser loading, weathervaning systems with non-stationary effects for the design of FLNG/FPSO installations, etc.
Demonstrating a Tidal Turbine Control Strategy at Laboratory Scale
Authors: Harrold Magnus , Bromley Peter , Broudic Merin , Clelland David
Published: October 2016

Ahead of the installation of a commercial tidal stream turbine, a 1:30 scale model of the device was tested in a recirculating flume tank. This proved to be the first physical demonstration of the turbine’s unconventional control strategy, which limits the thrust forces on the device by allowing the rotor to enter an overspeed. The tests showed that this simple to implement concept of operation is a cost-effective and reliable means of managing the rotor thrust loads in energetic flows. Subsequent tests highlighted the importance of correctly calculating the controller gain parameter, otherwise detrimental turbine performance characteristics can be expected. When relating these results to that of the commercial device, there are a number of important differences associated with both the environment and scale of the model tests. Despite this, the results are considered encouraging, and provided confidence for the full-scale deployment.
Characterization of Time-Averaged Turbulence Statistics for Shear Thinning Fluid in Horizontal Concentric Annulus Using RANS Based CFD Simulation
Authors: Xiong Xiao , Rahman Mohammad Azizur , Zhang Yan
Published: October 2016

A RANS based shear stress transportation (SST) model was employed in this study to validate experimental results from a recent literature, which investigated the fully developed turbulent flow for a non-Newtonian shear thinning fluid, containing drag reduction polymer additives in a horizontal concentric annulus (inner to outer radio θ = 0.4). The polymer concentration varied from 0.07% V/V to 0.12% V/V and three mass flow rates from 3.92 kg/s to 5.95 kg/s were analyzed. The viscous property of the fluid was modeled by the power-law model. Simulation performed with the commercial code of ANSYS-CFX indicated that the SST model with default model constants overestimated the turbulence statistics of shear thinning flow in the near wall region where y+<60. As an effort to improve simulation accuracy, one of the model constants α1 was tuned in this study for the first time. Simulation results obtained from the modified model showed better agreement with experimental data compared to those from the default one. The present study represents a successful benchmark task for simulating turbulent shear thinning flow in concentric annuli with modified turbulence model constants.
Equivalent Model for Interlocked Carcass Under Axial Loads
Authors: Provasi Rodrigo , Geremias Toni Fernando , de Arruda Martins Clóvis
Published: October 2016

The modelling of flexible pipe interlocked carcasses is complicated when considering all the geometric complexity of their profile. A possible approach is to model them as cylindrical equivalent layers. To follow this path several alternatives can be considered in changing the geometrical and material properties. However, the thickness and the mean radius of those layers must not be changed to not interfere with the diameter of the other flexible pipe layers.

In this paper, a model of an orthotropic cylindrical layer, with the same thickness and mean diameter of the original carcass layer is constructed and its material parameters are adjusted for axial loads using a finite element model of the real carcass profile.
CFD and EFD Based Studies of Hull Wetness of Fast Mono-WPC
Authors: Wei Chengzhu , Li Yinghui , Yi Hong
Published: October 2016

Fast mono-wave-piercing craft (Fast Mono-WPC) use a tumblehome design and run at high speeds. Efforts have been made to study hull wetness problems because of the special hull shape and running state of Fast Mono-WPC. Numerical and experimental methods were adopted to study hull wetness problems of Fast Mono-WPC both in calm water and waves. Numerical methods were based on RANS. Dynamic mesh methods were used to simulate model motions. Influence of velocity, spray strips and hull motions on hull wetness of Fast Mono-WPC in calm water was studied. Results of CFD and EFD in calm water show that hull wetness of Fast Mono-WPC is sensitive to hull motions such as heave and pitch, and spray strips on the bow can reduce hull wetness. Model tests in regular and irregular waves and numerical simulations in regular waves of a free Fast Mono-WPC model were conducted at a high Froude number, Fn = 0.815. Numerical results show that wetness is slight when Fast Mono-WPC runs in 1L-long and 4L-long waves, and water climbs up the freeboard to the deck when Fast Mono-WPC cuts through 2L-long waves. Serious hull wetness was also experimentally observed both in regular and irregular waves.
Breaking Load of Thick Ice on Sloping Structures
Authors: Teo Fwu Chyi , Poh Leong Hien , Pang Sze Dai
Published: October 2016

Sloping-sided structures have been used in ice-infested waters to reduce ice loads by inducing flexural failure in the incoming level ice, which can be a fraction of the crushing load of the same level ice on vertical walls [1]. Croasdale’s model [2] has been widely used to predict this type of ice loading, which compares well with available field data, such as that measured at the Confederation Bridge [3]. In Croasdale’s formulation, the problem is idealized as a semi-infinite beam on an elastic foundation and neglects the effects of second-order bending and the edge moment arising from eccentricity of axial loadings, i.e. the distance between the point of ice-structure contact and the centroidal axis of the beam. For thin ice, the edge moment effect is indeed negligible due to the small moment arm. However, the edge moment influence on the structural load increases with the ice thickness, as reported in [4]. This suggests that Croasdale’s model may be inadequate for ice thickness beyond a certain threshold. In this paper, we focus on the plane breaking load of thick ice, taking into account the second order bending of the beam as well as the edge moment effect. We also account for the local crushing of level ice that comes into contact with the sloping structure, which creates a surface parallel to the slope prior to the bending failure of ice sheet. This local crushing is assumed to occur until a sufficient surface area is created to provide the bearing capacity required to induce bending failure in the beam. As a result, the eccentricity of axial loading is reduced, lowering the effects of the edge moment and consequently, the predicted load. Taking the above effects into account, the governing equation and the corresponding deflection equation of the refined model are reformulated, and the system of non-linear equations solved with numerically with the Newton-Raphson method. Additionally, the competition between different failure modes, i.e. flexural, crushing and shear, of a level ice encountering a sloping structure is briefly investigated. It is shown that flexural failure remains the dominant mode of failure even for thick ice, for various practical slope angles, ice material properties and ice-structure contact properties.
Evaluation of Walk-to-Work Accessibility for a Floating Wind Turbine
Authors: Martini Michele , Jurado Alfonso , Guanche Raúl , Losada Iñigo J.
Published: October 2016

There is a growing interest from offshore and energy industry towards floating wind turbines. Since these systems are exposed to harsh metocean conditions, accessibility for inspection and maintenance purposes becomes of primary importance for a safe and cost-effective long-term operation.

It is here proposed a methodology for evaluating the accessibility of a floating wind platform, by means of walk-to-work vessels.

Two access means are considered: a catamaran equipped with fender and an offshore supply vessels with a motion-compensated gangway. The system composed by the platform and the vessel is modelled as a constrained multi-body system in the frequency domain. This allows to calculate transfer functions for the vessel motions and the contact forces.

For given a short-term sea state the maximum crest height of a response variable is calculated assuming that crests heights are Rayleigh distributed, and compared to some threshold to determine whether the platform is accessible or not. For the catamaran, access is possible when the fender does not slip against the landing structure mounted on the floating platform; for the supply vessel, when the relative motions at the gangway tip do not exceed the compensation limits of the hydraulic system. Accessibility is calculated for a sample semisubmersible wind turbine located off the coast of Portugal using hindcast data for the period 1980–2013. Findings indicate that the catamaran and the supply vessel can ensure access for 20% and 76% of the time respectively. However, results are strictly dependent on the vessel types and the walk-to-work constraints.
Technology Qualification of Extreme Fjord Crossings
Authors: Johansen Inger Lise
Published: October 2016

The objective of this paper is to describe a framework for technology qualification for extreme fjord crossings. The motivation and scope is the project coastal highway route E39, which requires use of groundbreaking technologies to replace ferry connections with bridges across eight challenging fjords in the western Norway. The paper identifies key uncertainties related to use of new technology for extreme fjord crossings, concerning rules and methodologies, environmental conditions and implications in terms of risk. It then identifies needs and challenges for technology qualification in order to reduce these uncertainties and demonstrate that the technology is ready for use. This provides the basis for a new framework for technology qualification of extreme crossings. The framework combines principles of a risk-based, goal-driven approach with predefined levels of technological maturity, which are linked to key decision gates in the development project.
Numerical Simulation of Irregular Wave Forces on a Horizontal Cylinder
Authors: Aggarwal Ankit , Alagan Chella Mayilvahanan , Kamath Arun , Bihs Hans , Arnsten Øivind Asgeir
Published: October 2016

In the present study, the irregular wave forces on a fully submerged circular cylinder are investigated using the open-source computational fluid dynamics (CFD) model REEF3D. A complete three dimensional representation of the ocean waves requires the consideration of the sea surface as an irregular wave train with the random characteristics. The numerical model uses the incompressible Reynolds-averaged Navier-Stokes (RANS) equations together with the continuity equation to solve the fluid flow problem. Turbulence modeling is carried out using the two equation k-ω model. Spatial discretization is done using an uniform Cartesian grid. The level set method is used for computing the free surface. For time discretization, third-order total variation diminishing (TVD) Runge Kutta scheme is used. Ghost cell boundary method is used for implementing the complex geometries in the numerical model. MPI is used for the exchange of the value of a ghost cell. Relaxation method is used for the wave generation. The numerical model is validated for the irregular waves for a wave tank without any structure. Further, the numerical model is validated by comparing the numerical results with the experimental data for a fully submerged circular cylinder under regular waves and irregular waves. The numerical results are in a good agreement with the experimental data for the regular and irregular wave forces. The JONSWAP spectrum is used for the wave generation. The free surface features and kinematics around the cylinder is also presented and discussed.
A Comparison of Simplified Engineering and FEM Methods for On-Bottom Stability Analysis of Subsea Pipelines
Authors: Ji Guomin , Li Lanjing , Ong Muk Chen
Published: October 2016

This paper presents a comparison between simplified engineering and FEM (Finite Element Method) methods for on-bottom stability analysis of a subsea pipeline. The simplified engineering method is first used to assess the absolute on-bottom stability of empty and filled pipelines under different scenarios. The calculations of the hydrodynamic loads for three scenarios, i.e. steady current alone, regular waves alone and combined regular waves and current, are implemented in MATLAB code. The drag and lift coefficients are determined based on Keulegan-Carpenter number, Reynolds number and surface roughness of the pipelines. Only the friction force is considered in the simplified methods. In order to achieve the absolute stability, the vertical (lift force/submerged weight<1) and horizontal (in-line force/friction force<1) criteria need to be fulfilled at same time. Time-domain dynamic on-bottom stability analysis is performed by PONDUS for the same cases. The results of water particle velocity, hydrodynamic force, lift force and soil resistance force are compared between the simplified engineering and advanced FEM methods. Their results are in good agreement for the cases, which fulfills the absolute on-bottom stability criterion. For the cases which the pipelines will move under the combined wave and current loadings, the soil resistance force predicted by the simplified engineering method is different from that of the FEM method. The study shows that for engineering purpose the simplified engineering method could be used to check the absolute on-bottom stability of the pipeline, whereas the more advanced FEM method needs be performed when the pipeline is allowed to move within a limited distance.
High Peak Strain on Pipeline Material During Reel-Lay: Acceptable or Not?
Authors: Karjadi Erwan , Smienk Henk , Thibaux Philippe , Aamlid Olav
Published: October 2016

The nominal strain occurring during installation of a pipeline by the reeling method is expected to be limited to 2–3% strain. This is only true if the pipeline has a perfect geometry (diameter, thickness) and homogeneous material properties along its length, resulting in a uniform bending stiffness. There will however always be a stiffness mismatch at the joints between pipes. Different scenarios can be considered as the cause of this stiffness mismatch: differences in average wall thickness and average yield stress of two pipe joints welded together, counterbored/machined pipe ends or field joint coating for pipes with thick coating. To some extent these scenarios can initiate high peak strains in the pipeline material far above the level of the expected nominal strain, exceeding in some cases 5% strain. Questions which might arise are: Could this high peak strain occurrence be ignored?, or: What is the impact of the high peak strain on the performance of the material after reeling?

This paper presents FEA results illustrating the concerns of the occurrence of large peak strains which can still be significant even after averaging these strains over the thickness as well as over a certain length of the pipe. The methodology of averaging strains, as proposed together with DNV GL, correlates the length of the averaging pipe section with the maximum length of the test specimen geometry as allowed when performing strain aging tests of specimens with high tension and compression strains. A series of cyclic plastic deformation tests with pre-strained specimens from 4% to 7% strain was performed with seamless pipe material, followed by the tensile, Charpy and hardness tests of strain aged samples. One of the challenges is the setup of the test machine to avoid buckling of specimens during high compression pre-straining.

The results from material tests (tensile, hardness and Charpy) have been evaluated against the DNV-OS-F101 Supplementary requirement for plastic deformation (P). The consequences of material modification due to plastic strain is further discussed and evaluated referring to the DNV GL limit state design and criteria for pipeline installation after reeling as well as during the lifetime of the pipeline.
Floating Bridge Technology: Prediction of Extreme Environmental Load Effects
Authors: Villoria Bruno
Published: October 2016

The present paper describes the different concepts considered for the crossing of Bjørnfjorden. The emphasis is put on the methodology implemented for the estimation of the extreme environmental loads the chosen structure will be exposed to.
On Autocorrelation of Ice Loads, Measured in Ice Tank Experiments
Authors: Zvyagin Petr
Published: October 2016

Temporal dynamics of ice loads, which are measured with high sampling rate in experiments in ice tank, usually show strong autocorrelation. At the moment it is lack of study on autocorrelation function (ACF) of ice loads time series. In this paper the stochastic processes approach will be applied to analyze autocorrelation of ice loads.

Stochastic models for ice loads, developed earlier by the author, allow determining the distribution law and stationarity (in wide sense) for some of such time series in statistically confident manner. That allows conducting further study of those time series ACF.

For analysis and correct sampling rate choice it is important to know the time interval, which separates two statistically independent data points in time series. The algorithm for finding of such interval for time series with normal and lognormal distribution was developed in the paper. That algorithm was applied to find independence distance for global loads records, obtained in experiments with cylindrical models in ice tank of Krylov State Research Centre (St. Petersburg). The independence distance for those time series occurred to be 0,07–0,35 sec. That distance had increased with increasing of indenter diameter. Obtained results are discussed.
Design and Underwater Tests of Subsea Walking Hexapod MAK-1
Authors: Chernyshev Vadim V. , Arykantsev Vladimir V. , Gavrilov Andrey E. , Kalinin Yaroslav V. , Sharonov Nikolay G.
Published: October 2016

An important role among machines for sea bottom exploration is assigned to the autonomous ground devices. Some rescue tasks also require subsea robotic devices. The main purpose of the work is to investigate and improve adaptive characteristics, traction properties and control methods of cyclic walking movers in underwater conditions. Traction properties of walking machines, which moves at sea bottom was analyzed. Some experience of development and experimental tests of the walking robot “Vosminog”, designed for work at weak and waterlogged grounds. Dynamic model of a walking machine has been shown. Studied an opportunity to increase adaptive characteristics and shape passableness of walking machines. Also design and results of underwater tests of subsea walking unit MAK-1 are discussed. During tests the performance of a walking unit has been checked and the influence of design features of a walking mover on its traction characteristics and ground passability has been investigated. Some details about control system, power system and energy usage, vertical motions and accelerations for different types of walking and conditions of movement has been given. Also, certain attention was given to testing of methods of standalone movement control of subsea unit in conditions of incomplete and ambiguous vision of current situation. Tests have shown that walking movers in subsea conditions can provide higher traction properties, in comparison with wheeled and tracked ones. The unit can be used for exploration of seabed resources and for rescue tasks.
Ultimate Strength of Typical Stiffened Panels in Container Ships Under Localized Pitting Corrosion
Authors: Cui Jinju , Wang Deyu , Ma Ning
Published: October 2016

In the life cycle of ships, corrosion exists and deteriorates ship structures, resulting in the degradation of ship structural capacity. Based on practical observations, non-uniform corrosion takes place instead of uniform corrosion which is adopted widely in design rules. So it is necessary to 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 localized pitting corrosion is studied by Nonlinear Finite Element Analysis (NFEA). The pitting corrosion is supposed to be of normally distributed circular shapes whose radius is in accordance with observational statistics. Different pitting corrosion densities with perforation in both the stiffener and panel plate are considered. Structural ultimate strengths under pitting corrosion are studied under longitudinal loads, transverse loads and combination of both, and the results are compared with that from equivalent uniform corrosion. Finally, the probabilistic characteristics of structural ultimate strength under pitting corrosion in life cycle are studied.
CFD Modeling of Heat Transfer in Oil Filling and Offloading of SDPSO Storage Tank
Authors: Liu Dongxi , Gu Hong , Wang Jin , Tang Wenyong , Liu Weiwei
Published: October 2016

A deepwater Spar Drilling Production Storage Offloading (SDPSO) floating system that consists of a classic Spar hull with dry–tree production, oil storage and offloading has been proposed for offshore oil exploitation. One of the key features of the SDPSO is the oil storage system, which includes the mid–section of the classic spar hull for oil storage providing a large storage capacity of more than 500,000 barrels of oil. In the working condition, oil storage tank is fully filled with oil and seawater, the storage and offloading of oil are achieved by seawater displacement and oil–water separation. However, a seawater displacement oil storage system does raise the problems of stability of the oil–water interface, possible sludge contamination of the water and corrosion of the internal surface of the storage tank during oil filling and offloading operations. It is clear that sludge deposit and corrosion effect are closely related to the temperature distribution of crude oil and seawater inside the tank. Therefore, it is necessary to investigate hot–oil/cold–water heat transfer in the SDPSO oil storage tank during both operations and storm conditions. For this purpose, CFD modeling and numerical studies were performed for a simplified oil storage system of the SDPSO platform in an effort to gain better understanding of the heat transfer problem.
Numerical Calculation of Roll, Pitch and Heave Decay of a Gravity-Based Structure During Tow-Out
Authors: Ciortan Cosmin , Johnsgard Helge , Overstake Meg , Rognebakke Olav , Brehm Andreas
Published: October 2016

ExxonMobil Canada Properties and its collaborators are building a gravity based structure (GBS) in Newfoundland and Labrador to be installed on the Hebron Field offshore Eastern Canada. The geometry of the Hebron GBS is driven by the design constraints of a long operating life placed on the seafloor in the harsh environments at the Hebron field location. Prior to installation, the GBS encounters a number of significant floating phases — deep-water construction, towage, and installation. In each of these stages the hydrodynamic character of the unique Hebron geometry must be quantified to predict dynamic motions, assess tow performance, and define installation procedures and limitations. For the floating GBS, both heave and roll natural periods are long, and resonant responses due to wind gusting and vertical wave drift take place. Assessing the hydrodynamics by industry standard empirical methods is insufficient as regards capturing the viscous damping generated by eddy formation off the sharp edges of the submerged GBS structure. This paper focuses on the utilization of Computational Fluid Dynamics (CFD) to better understand and quantify this viscous damping. The Hebron GBS work has challenged the traditional methods for model generation and use of CFD for damping estimation, primarily because these techniques are most frequently used for traditional hull shapes. For example, application of the overset mesh technique, as successfully applied for ship-shaped vessels, does not provide the required accuracy in this case. Alternative numerical models are tested and found to work well: morphing techniques and sliding meshes for heave and pitch, respectively. Based on convergence and sensitivity studies, the results are accepted. Ultimately, the CFD work allows the project to quantify the expected increases in hydrodynamic damping and progress in the process of improving predictions of GBS motions and thus optimizing the operational planning of towing and installation.
H2S Consumption and the Derivation of a New Annulus Prediction Model for Offshore Flexible Pipes
Authors: Haahr Marie , Gudme Jonas , Sonne Jacob , Overby Sten , Nielsen Torben , Rubin Adam
Published: October 2016

This paper presents the outcome of investigations on the effects of H2S consumption in the annulus of a flexible pipe. Low-molecular gases, such as CH4, H2S, H2O and CO2, permeate slowly from the bore through the inner liner into the annular space between the inner liner and outer sheath of a flexible pipe. This space is densely packed with carbon steel armour wires leaving a very limited free volume. In the presence of water, a corrosive environment for the armour wires is generated and a risk of sour service cracking is introduced. H2S concentration in the annulus is traditionally calculated by balancing the inflow through inner liner and the outflow through outer sheath and vent valve.

In order to assure H2S resistance of the armour wires towards calculated H2S concentrations, pipes for sour service are typically designed with lower strength wire grades of larger dimensions compared to the possibilities of sweet service pipes. Over the last decade, more and more offshore data has been obtained indicating considerably less H2S in the annulus than predicted by the traditional annulus models.

This observation has triggered in-depth investigations of the complex corrosive H2S environment inside a flexible pipe annulus exposed to sour service conditions. An extensive small-scale test program has been conducted and showed that at permeation rates typical for flexible pipes, the consumption of H2S in the corrosion processes occurring in the annular space lowers the concentration and hence criticality of the H2S so significantly that it leaves the traditional models overly conservative to an extreme extent.

Using this knowledge of consumption of the corrosive gases in the annulus has become an increasingly important topic with the focus on deeper waters, cost savings and service life extensions without compromising flexible pipe integrity.

Based on experimental data obtained, a new annulus model for prediction of H2S pressure in annulus has been derived. Data is presented in this paper to illustrate the methodology for an annulus prediction where the consumption of H2S is included. The data presented covers laboratory tests with variations and effects of gas flux, H2S concentration and total pressure. A full-scale validation, led to an Independent Verification Agency certification of the model.

With the introduction of this new annulus prediction model, a wider range of wire products becomes available for the pipe designers. Lower weight pipes with stronger armour wires render optimizations for both cost savings and applications at deeper waters possible.
On-Line Phased-Array Ultrasonic System: OPUS to Control Pressure Sheath of Flexible Pipe During Manufacturing
Authors: Mélot Mickaël , Berthon Julien
Published: October 2016

Flexible pipes are made up of several different layers specifically designed to meet the requirements of our clients and API17J / ISO13628-2. In the pursuit of ever more efficient and reliable solutions, even in the world’s harshest and deepest offshore environments, TECHNIP’s R&D activity is focused on extending its product range by introducing new products and materials. As part of this innovation program, new polymers are constantly being investigated to assess their potential as a pressure sheath.

The pressure sheath is the most critical thermoplastic sheath within the structure. Its role is to contain internal fluid and transfer internal pressure to the pressure vault layer outside it. To fulfill that mission, this polymer must be leakproof and perform over wide temperature and pressure range. In operation condition, the presence of small flaws within the pressure sheath could propagate leading to failure and significant environmental and operational damages. Therefore, the manufacturing of such a polymer layer must conform with ever-higher levels of reliability and quality. This is the reason why a visual inspection of pressure sheath according to API17J / ISO13628-2 standards is mandatory.

As a leitmotiv, TECHNIP dedicates a lot of effort, not only to extend the limits of the possible by introducing new materials, but also to take inspection further beyond standard requirements by developing dedicated on-line NDT control systems able to ensure layer high quality. Many people are familiar with the medical applications of ultrasonic imaging in which ultrasonic waves are used to create highly detailed cross-sectional pictures of internal organ. Medical echography is commonly performed with specialized multielement probe known as phased-array and their accompanying hardware and software. The applications of ultrasonic phased-array technology are not limited to medical diagnosis and in recent years, increasing use of these systems can be observed in industrial environment. Nevertheless, although phased-array systems on the market can provide new levels of information and visualization, they are manually and locally operated and are inappropriate to control polymer sheath over several kilometers during manufacturing.

This paper presents a specific and automated ultrasonic system dedicated to manufacturing control of thermoplastics such as the pressure sheath. Developed by TECHNIP, and based on cutting edge ultrasonic technology used in aerospace and medicine, OPUS is a world-class NDT system able to prove that our pressure sheaths meet design criteria and achieve the highest quality level.
CFD-Based Numerical Wave Basin for Global Performance Analysis
Authors: Wu Guangyu , Kim Jang Whan , Jang Hyunchul , Baquet Aldric
Published: October 2016

Several recent benchmark studies have demonstrated that Computational Fluid Dynamics (CFD) is capable of capturing both nonlinear and viscous effects in offshore marine hydrodynamics and predicting well certain wave- and current-induced offshore platform motion. In order to apply CFD for practical global performance analysis of a complete hull-mooring-riser coupled floating system, we develop an advanced numerical wave basin that combines CFD, nonlinear irregular wave modeling, and finite-element mooring modeling. Specifically, CFD is used to simulate the violent free-surface flow with hull motions; nonlinear wave modeling is applied to generate a realistic wavefield and provide initial and far-field conditions to CFD for efficient long-duration simulation; and mooring modeling is two-way coupled with CFD to account for dynamic mooring response and its effects on hull motion. In this study, to demonstrate the capability of such tool, the global performance of a semi-submersible with 4 mooring lines in a 3-hour extreme sea state is simulated for both head and quartering sea. The simulation results are compared to model test data of hull motion, mooring line tension, and relative wave elevation around the hull for validation. It is shown with spectrum and statistics that the simulations predict well the platform’s global performance in all frequency ranges, including low frequency where the mooring lines have the greatest influence on the motion response. Compared to the predictions from a conventional global performance design tool that is based on diffraction analysis and empirical coefficients, the CFD results show significant improvements. The encouraging results from this study indicate that a CFD-based numerical wave basin, although still computationally expensive, is technically ready to be a complementary tool to physical wave basin for offshore platform global performance design.
Failure Prediction of Fiber Reinforced Laminated Composite Plates Under Low Velocity Impact
Authors: Patel Shivdayal , Ahmad Suhail
Published: October 2016

The low velocity impact on composites has been studied as it leads to serious damage. The damage initiates as an intra ply matrix crack due to shear or bending which propagates further into the interface causing de-lamination between dissimilar plies and fiber breakage. This damage evolves with time and adversely affects the mechanical properties and strength of the composite. Since, multiple cracks in the ply are difficult to track, a progressive damage mechanics approach is used to model this failure. The inter ply failure is modeled using cohesive surfaces between the plies. The low velocity impact on composite plate is studied using finite element method. Impact parameters like velocity of impactor, the mass of the impactor and elastic properties of the material etc. are considered. An explicit central difference integration scheme is used to solve for displacements and impact forces.

Progressive damage and failure in composites is modeled; an efficient algorithm has been developed and implemented in the FE code ABAQUS through a user-defined subroutine (VUMAT). Reduced integration yields satisfactory results for the impactor velocity less than or equal to 3 m/s for larger mass impact. However, full integration is recommended to obtain the satisfactory results for the (impactor velocity beyond 3 m/s), high velocity impact involving small masses. For the low velocity impact, the peak contact force and displacement are linear functions of impactor velocity for a constant mass. However, a nonlinear behavior is observed for the variation of mass with a constant striking velocity.
Model Test and Numerical Analysis of an Offshore Bottom Fixed Pentapod Wind Turbine Under Seismic Loads
Authors: Wang Wenhua , Gao Zhen , Li Xin , Moan Torgeir , Wang Bin
Published: October 2016

In the last decade the wind energy industry has developed rapidly in China, especially offshore. For a water depth less than 20m, monopile and multi-pile substructures (tripod, pentapod) are applied widely in offshore wind farms. Some wind farms in China are located in high seismicity regions, thus, the earthquake load may become the dominant load for offshore wind turbines.

This paper deals with the seismic behavior of an offshore wind turbine (OWT) consisting of the NREL 5MW baseline wind turbine, a pentapod substructure and a pile foundation of a real offshore wind turbine in China. A test model of the OWT is designed based on the hydro-elastic similarity. Test cases of different load combinations are performed with the environmental conditions generated by the Joint Earthquake, Wave and Current Simulation System and the Simple Wind Field Generation System at Dalian University of Technology, China, in order to investigate the structural dynamic responses under different load conditions. In the tests, a circular disk is used to model the rotor-nacelle system, and a force gauge is fixed at the center of the disk to measure the wind forces during the tests. A series of accelerometers are arranged along the model tower and the pentapod piles, and strain gauges glued on the substructure members are intended to measure the structural dynamic responses. A finite element model of the complete wind turbine is also established in order to compare the theoretical results with the test data.

The hydro-elastic similarity is validated based on the comparison of the measured dynamic characteristics and the results of the prototype modal analysis. The numerical results agree well with the experimental data. Based on the comparisons of the results, the effect of the wind and sea loads on the structural responses subjected to seismic is demonstrated, especially the influence on the global response of the structure. It is seen that the effect of the combined seismic, wind, wave and current load conditions can not be simply superimposed. Hence the interaction effect in the seismic analysis should be considered when the wind, wave and current loads have a non-negligible effect.
Prediction of Riser VIV With Staggered Buoyancy Elements
Authors: Wu Jie , Lekkala Malakonda Reddy , Ong Muk Chen
Published: October 2016

Steel lazy-wave riser (SLWR) are attractive deepwater applications for offshore oil and gas industry. When subjected to current, both the buoyancy elements and the riser may experience Vortex Induced Vibrations (VIV). Such vibrations are the result of the periodic hydrodynamic forces that are induced by the interaction of slender bodies and external fluid flow. If the vibration period is close to the natural period of the system, it can lead to fast accumulation of fatigue damage to the risers and amplified drag loads. There is a competition between the vortex induced forces acting on the buoyancy element and the riser segment due to its different diameters. The interaction of the vortex shedding from the riser and the buoyancy element depends on many parameters, such as the arrangement of the buoyancy element, aspect ratio of the buoyancy element, etc.

Shell Oil Company conducted VIV model tests with a straight flexible cylinder and staggered buoyancy elements corresponding to a buoyant section of a SLWR in MARINTEK in 2011. Five different buoyancy element configurations were tested. The test data has been extensively studied (Rao, et al 2015 and Jhingran, et al 2012). The interaction of the buoyancy elements and bare riser and its influence on the riser response (frequency, displacement and fatigue damage) have been investigated.

Semi-empirical VIV prediction software, such as VIVANA [4], SHEAR7 [13] and VIVA [11] are most commonly used by the offshore industry in the riser systems design against VIV loads. However, these software are not purposely designed to account for the interaction of the bare riser section and the buoyancy elements. It is of great interest to evaluate the prediction accuracy. The purpose of this study is to benchmark the VIV prediction of riser with buoyancy elements using VIVANA. The prediction is compared with Shell model test results with focus on CF responses. Uncertainty and improvement of the prediction are also discussed.
Potential Impact of Sudden Change of Wind Condition on Offshore Operation
Authors: Lu Yongjian , Ozaki Masahiko
Published: October 2016

The emphasis in this paper is to investigate the potential impact on offshore operation caused by the sudden change of wind condition. First, a questionnaire survey was conducted on experienced operation workers in Japan. The results show 74% respondents have experienced the danger of sudden change of wind condition in offshore operation. It is found that both the operation on board and the motion of ship can be affected by sudden change of wind condition.

One-dimensional time-domain simulations are done to understand the performance of dynamic positioning system (DPS) when suffering from sudden change of wind condition. Squall models are determined on the basis of real cases on the sea near Japan. The results show an operation ship with PD control cannot keep its positioning in the allowable operation zone if the peak of wind speed exceeds more than a certain degree of the designed value. Wind feedforward can decrease the ship’s maximum displacement only with a short measurement interval. Adding integral control to the DPS can also achieve the ship staying in its allowable zone but bring severe destabilization. The jointed effects of unbefitting wind feedforward and PID control may make the ship more difficult in dealing with the squall in a short time. By using the Davenport spectrum, squall models are turned into fluctuating wind form. The gust with higher speed than the mean wind speed appears. However, it does not affect the performance of the DPS. It also illustrates that squall, a sudden change of wind condition in a relatively long time, can bring effects on DPS with motion outside its control. This will result in negative effects on offshore operation.
Evaluation of Ultimate Hull Girder Strength in Longitudinal Bending: Historical Review and Smith’s Method
Authors: Yao Tetsuya
Published: October 2016

Ultimate hull girder strength in longitudinal bending is the most important strength of ship structure. In the present paper, firstly, historical review is made regarding the research activities regarding the ultimate hull girder strength evaluation. Then, focusing on the Smith’s method, possibility of simplified method is discussed including what are the limitations of a simple method and how it can be extended to more general situation. A simple method is introduced to derive average stress-average strain relationships of stiffener elements with attached plating. At the end, results of some example calculation are introduced to demonstrate the effectiveness of a simple method for progressive collapse analysis of a ship hull girder.
A Numerical Study on Wave Propagating Through In-Line Net Cages
Authors: Zhao Yun-Peng , Bi Chun-Wei , Dong Guo-Hai , Bai Xiao-Dong , Xu Tiao-Jian
Published: October 2016

A three-dimensional numerical model is established to simulate the interaction between waves and net cages. The porous-media fluid model is introduced to model the net cage in waves. An oscillating-boundary method is used to generate waves at one end of a tank partially filled with water. The flow motion of an incompressible, viscous fluid is described by Navier-Stokes equations and the free surface is tracked by volume of fluid (VOF) method. Validation of the numerical model is conducted by comparing the numerical results with the corresponding physical-model measurements of a net-cage model. In order to visualize the wave field around in-line net cages, numerical results of both wave elevation and water-particle-velocity distribution on a vertical plane of a transient field are presented. Compared with the undisturbed wave field, the effects of the net cages on both the wave elevation and the water-particle-velocity distribution around the net cages are noticeable. The study will contribute to understanding of the damping effect of a large fish farm on wave propagation.
Application of Industry Guidelines, CFD and Frequency Domain Analyses to Assess Flow Induced Vibration Risk in Pipework
Authors: Fielding David , Graham Alex , Shorter Phil
Published: October 2016

This paper presents currently available methods for assessment of flow-induced vibration (FIV). Approaches considered include the application of the Energy Institute’s guidance [1], as well as advanced simulation; where flow simulation using computational fluid dynamics (CFD) and structural response using finite element (FE) analysis are coupled. Using a test case where initial screening by the guidelines results in a recommendation for further analysis, an approach using both CFD and vibro-acoustic analysis is described. This process enables the practitioner to quantify the different vibration mechanisms present, as well as to understand the risk of fatigue failure and what corrective action, if any, is required.
Scaling Analysis for the Liquefaction Phenomena Induced by Water Waves
Authors: Arcos E. , Bautista E. , Méndez F.
Published: October 2016

In this work an scaling analysis of the liquefaction phenomena is presented. The characteristic scales are obtained by balancing term by term of the well known partial dynamics governing equations (approximation U – P). The order of magnitude of the horizontal displacement are very smaller compared with the vertical displacement and therefore the governing equation are only a function of the dependent vertical variables. The U – P approximation is reduced and presented in its dimensionless version. This scaling analysis can be used to obtain analytical solutions of the liquefaction phenomena under the action of the water waves.