bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
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.
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.
A Review on Damage Identification and Structural Health Monitoring for Offshore Platform
Authors: Sun Liping , Lu Yang , Zhang Xinyue 
Published: October 2016

Structural health monitoring (SHM) based on vibration measurements in large/complex structures were shown to be promising by researchers. The authors believe that the SHM problem is fundamentally one of statistical pattern recognition. Therefore, the damage detection studies reviewed herein are summarized in the context of a statistical pattern recognition paradigm[1]. This paradigm can be described as a three-part process: (1) Data acquisition and cleansing, (2) Modal parameter identification, (3) Damage identification methods. However, offshore platform structures are very complex, and not easy to excite artificially and they are often suffered from ambient loads that cannot be controlled easily. The thesis focuses on three key issues for structural health monitoring via vibration in real offshore platform structures[2].
In the first part of review, the offshore platform structure health monitoring system basic principle and the composition are discussed. In the second portion, three important processes of structure health monitoring are summarized (Data acquisition and cleansing, modal parameter identification, damage identification methods), and each method good and bad points is pointed out. Next, Application of damage identification and structural health monitoring to offshore platform are in detail produced, the methods are described in general terms including difficulties associated with their implementation. Finally, current and future-planned applications of this technology to offshore platform are summarized. The paper concludes with a discussion of critical issues for future research on damage identification and structural health monitoring for offshore platform.
A FEM Based Potential Theory Approach for Optimal Ice Routing
Authors: Piehl Henry , Milaković Aleksandar-Saša , Ehlers Sören 
Published: October 2016

Shipping in ice covered regions has gained high attention within recent years. Analogous to weather routing, the occurrence of ice in a seaway affects the selection of the optimal route with respect to the travel time or fuel consumption. The shorter, direct path between two points — which may lead through an ice covered area — may require a reduction of speed and an increase in fuel consumption. A longer, indirect route, could be more efficient by avoiding the ice covered region. Certain regions may have to be avoided completely, if the ice thickness exceeds the ice-capability of the ship.
The objective of this study is to develop a computational method that combines coastline maps, route cost information (e.g. ice thickness), transport task and ship properties to find the optimal route between port of departure A and port of destination B.
The development approach for this tool is to formulate the transport task in form of a potential problem, solve this equation with a finite element method and apply edge detection methods and line integration to determine the optimal route. The functionality of the method is first evaluated with simple test problems and then applied to realistic transport scenarios.