bluuebunny/crossref_metadata_2025_split huggingface dataset:
Computation of Nonlinear Hydrodynamic Loads on Floating Wind Turbines Using Fluid-Impulse Theory
Authors: Chan Godine Kok Yan , Sclavounos Paul D. , Jonkman Jason , Hayman Gregory 
Published: October 2015

A hydrodynamics computer module was developed to evaluate the linear and nonlinear loads on floating wind turbines using a new fluid-impulse formulation for coupling with the FAST program. The new formulation allows linear and nonlinear loads on floating bodies to be computed in the time domain. It also avoids the computationally intensive evaluation of temporal and spatial gradients of the velocity potential in the Bernoulli equation and the discretization of the nonlinear free surface. The new hydrodynamics module computes linear and nonlinear loads — including hydrostatic, Froude-Krylov, radiation and diffraction, as well as nonlinear effects known to cause ringing, springing, and slow-drift loads — directly in the time domain.
The time-domain Green function is used to solve the linear and nonlinear free-surface problems and efficient methods are derived for its computation. The body instantaneous wetted surface is approximated by a panel mesh and the discretization of the free surface is circumvented by using the Green function. The evaluation of the nonlinear loads is based on explicit expressions derived by the fluid-impulse theory, which can be computed efficiently.
Computations are presented of the linear and nonlinear loads on the MIT/NREL tension-leg platform. Comparisons were carried out with frequency-domain linear and second-order methods. Emphasis was placed on modeling accuracy of the magnitude of nonlinear low- and high-frequency wave loads in a sea state. Although fluid-impulse theory is applied to floating wind turbines in this paper, the theory is applicable to other offshore platforms as well.
Assessment of the Commercial and Safety Limitations of High Capacity Reel Drive Systems vs Under-Rollers for Reel-Based Product Installation
Authors: Dale Nicholas 
Published: October 2015

Flexible products are becoming ever longer and larger to cope with the technical demands of deepwater fields and tie-backs. The implication of this being that product reels are becoming larger, heavier and more complex to manage during installation and recovery operations.
This paper explores the current limits of reel-based installation equipment evaluating the implications of the increased deck footprint, the necessity for modularity from an equipment repositioning and handling perspective and the limitations placed on vessel selection and vessel stability during installation. The safety, engineering, operability and commercial factors associated with each area of development are analysed to produce a complete snapshot of where the current industry limits lie and how far we can push the envelope for this method of installation.
Specific equipment focus is placed on reel-drive systems which are the industry standard and under-roller systems which, although represent a more dated technology, are still accepted in certain regions for flex lay operations.
Met-Ocean Conditions Influence Over Floating Wind Turbine Energy Production
Authors: Martini Michele , Guanche Raúl , Armesto José A. , Losada Iñigo J. 
Published: October 2015

The operation of a floating wind turbine may be severely affected by met-ocean conditions. In harsh climates, platform motions might exceed their safety limits and thus force the machine shutdown. It is here proposed a methodology for evaluating the effect of met-ocean conditions on the long-term energy production and dynamic response of such machines.
Given a sample wind turbine, located off the coast of Santander, Spain, met-ocean data are extracted from reanalysis databases for a twenty years lifespan.
The behavior of the wind turbine is simulated in the time domain for a subset of 500 hourly conditions, selected using a maximum dissimilarity algorithm (MDA), to reduce the computational effort. Results regarding floating platform motions are then interpolated for the whole set of data using radial basis functions (RBF).
Tower inclination and hub acceleration are selected as relevant operating parameters. When one of them exceeds its safety threshold, the machine is supposed to be stopped. If no stops are considered, the capacity factor is 39%, while imposing more restrictive tolerances results in a non-linear decrease of the energy yield.
This approach can be helpful in determining a good tradeoff between energy production and reliable operation, bridging the design and operational phases of the project.
Distributed Damping of Tsunamis
Authors: Javanmardi Mohammadreza , Alam M. Reza 
Published: October 2015

Tsunamis are a major threat to coastal communities. One of the ways to avoid tsunami disasters is to use breakwaters to attenuate the incident tsunami energy. The incident tsunami energy is expected to be dissipated by induced wave breaking in the shallow water over the structure peak.
In this paper, a new method to attenuate the tsunami energy is described and investigated. This new concept dissipates tsunami energy by implementing small barriers into the water before the tsunami reaches the shore. The interaction of tsunami-like solitary waves with new submerged barriers has been investigated and their performance was compared with that of conventional breakwaters. We found that the new structure can be used as a tsunami wave attenuator.
Real Time Estimation and Prediction of Wave Excitation Forces on a Heaving Body
Authors: Ling Bradley A. , Batten Belinda A. 
Published: October 2015

Wave energy converters (WECs) face many technical challenges before becoming a cost-competitive source of renewable energy. The levelized cost of electricity could be decreased by implementing real-time control strategies to increase average power produced by a WEC. These control strategies typically require knowledge of the immediate future excitation force, caused by the waves. This paper presents a disturbance prediction methodology that is independent of the local wave climate and can be implemented on a wide range of devices.
A time-domain model of a generic heaving WEC is developed with the Cummins equations. The model is simulated with measured water surface elevation data collected off the Oregon Coast. A simplified linear frequency-invariant state-space model is used in conjunction with a Kalman filter to estimate the current excitation force with measurements of the WEC’s motion. Future excitation forces are then predicted multiple steps in the future with a recursive least squares filter. The results show this approach makes accurate predictions of excitation force over short time horizons (up to 15 seconds), but accurate predictions become infeasible for longer horizons.
Metal Loss: Corrosion Defects Qualification and Structural Integrity Assessment
Authors: Gentile Manuela , Laudonia Ciro Antonio , Marchionni Lorenzo , Parrella Antonio , Vichi Roberta , Vitali Luigino 
Published: October 2015

The management of the flow availability in presence of corrosive fluids may considerably impact on CAPEX and OPEX of offshore pipelines. A correct approach starts from the preliminary phases of a project, with the selection of the most appropriate material in relation to the nature of the corrosive fluids and expected degradation mechanisms (i.e. general corrosion, localized or mesa corrosion and pitting). The construction phases include measures that allow meeting welding requirements and safe guarding the integrity of the line-pipe. The operation shall account for the control of process parameters and transported fluid composition.
In the upcoming future offshore pipeline and field development projects, challenging operating conditions in deep/ultra-deep waters means that increasingly careful considerations on the effect of metal loss: corrosion leading to local loss of material may cause a potential pipeline failure under the additional effect of functional and environmental loads, in particular the high external pressure and applied bending moment. The assessment of the structural integrity depends on the type and accuracy of available measurements. In presence of corrosion patterns and accordingly to existing standards (DNV RP-F101, ASME B31G, API 579, BS 7910) the assessment might be unduly conservative; further the presence of important combined loads is not fully covered by standard assessment format.
The use of FEM numerical lab can help the evaluation of the residual strength and deformation capacity of the pipeline affected by corrosion, leading to a quite-deterministic characterization of pipeline strength capacity at design stage and in operation. Several studies (both theoretical and experimental) available in the open literature faced this issue and their findings support the proposed analysis methodology. Recently full scale tests have been conducted by the relevant Oil & Gas industry companies (such as Statoil and ENI) and the obtained results have been used for the FE Model calibration and validation of corroded pipelines. Herein an application is presented in order to understand and appreciate the proposed methodology performance in corroded pipeline assessment.
In-Service Buckling Assessment: The Correct Use of Engineering Analysis Tools
Authors: Bartolini Lorenzo , Marchionni Lorenzo , Tassetti Sara , Battistini Alberto , Vitali Luigino 
Published: October 2015

There is consensus on the need for in-service buckling analyses to assess the integrity of both flowlines and long distance trunklines subject to HP/HT service condition. The extent of the analyses and supporting survey depends on the severity of the application.
In the last two decades, the pipeline industry has gained significant experience in both the design and operation of pipeline systems exposed to global buckling. Actually, the early 90s have been a watershed: before the phenomenon was just known (theoretically), then it was seen...as soon as pipeline integrity management programmes have been introduced in the offshore pipeline industry practices. Although, limited information have been documented in the open literature, now as then.
Several efforts have been dedicated to develop design methods and procedures suitable for operating pipeline safely as well as protecting the population, environmental resources and assets. At the beginning, there was a gap to be closed as specific mitigation measures were never designed. Nowadays, thanks to computational progress, it seems that the attention is addressed to face the uncertainties affecting the subject matter but, sometime, leading to overdesign.
The scope of the paper is to present aspects of global buckling design analyses that were performed in recent projects with the aim to highlight the challenges and the risks, the accuracy or the limitation of the methods, the feedback and the lesson learnt of real installed pipelines under operating conditions.
VIV Basics for Subsea Spool/Jumper Design
Authors: Bruschi Roberto , Bartolini Lorenzo , Molinari Caterina , Vignati Giulio C. , Vitali Luigino 
Published: October 2015

Coming and future Deep and Ultra-Deep Water project developments involve the use of many Subsea Rigid Jumpers used to connect well heads, manifolds or riser base with Flowline End Terminations.
Generally, Subsea Rigid Jumpers are short and flexible pipe sections assembled in a variety of spatial configurations to accommodate the installation tolerances, the Flowline End Terminations translation and settlement guaranteeing the continuity and the flexibility needs of the subsea pipe layout. These Subsea Rigid Jumpers are critical components as they are subject to fatigue damage due to Vortex Induced Vibrations induced by the bottom currents and/or Flow Induced Vibrations induced by the high internal flow rate, often coupled with slugging flow conditions.
In this paper, a Subsea Rigid Jumper design approach based on basics of Vortex Induced Vibrations is presented, and outcomes on a few typical multi-planar Subsea Rigid Jumpers discussed.
Spectral Strength Analysis of a Transportation Barge
Authors: Jedruszek Krzysztof , Meskers Geert 
Published: October 2015

Heerema Marine Contractors has been awarded contracts for the transport and installation of two ultra-heavy platforms — Arkutun Dagi and Wheatstone. The total transportation weight including deck support frame is about 45,000 mT for both of these projects. It requires the largest transportation and float-over barge in the world (H-851) and pushes it to the limit of its strength. A detailed study has been performed to verify the structural integrity of the barge. The design stresses have been determined using a spectral analysis, based on stress RAOs for each of the elements in the FEM model. All elements are tested against relevant code, looking at requirements for strength as well as buckling capacity. The advantage of the spectral strength analysis is that no assumptions need to be made about the most critical acceleration and the associated design wave. The method focusses directly on finding the critical stresses.
This paper explains the steps taken to perform a spectral strength assessment of a transportation vessel. It shows how stress RAOs are determined by combining results of a hydrodynamic analysis with a full scale FEM model. The stress RAOs are used to perform a strength and buckling verification using a full wave spectrum and results are related to the outcome of a design wave analysis performed by a third party. Explanations are provided based on Arkutun Dagi project.
New Extreme Model Applied to Mooring System Design Load Case Assessment
Authors: del Jesus Fernando , Guanche Raúl , Losada Íñigo J. , Vidal César 
Published: October 2015

Offshore wind energy turbines are being deployed massively in the North Sea. Most of the latest developments are monopile based due to the local bathymetry. However, future offshore wind farms will be located at larger water depths. Mainly because the nearest sites to the shoreline will be already occupied, future wind farms will be in 60 m water depth at least. This is, approximately, the limit for fixed support structures, such as monopiles, tripods and jackets. Some developers have already identified this need and some prototypes are under testing, such as WindFloat and Hywind.
Floating wind technology will face some challenges. One of the most important ones is how to moderate the cost of the platform and the mooring system. Consequently, it is necessary to reduce the uncertainty during design steps.
In this paper, new extreme mixed model will be applied to mooring system design. This extreme model combines instrumental and reanalysis data in order to obtain more accurate design parameters, reducing the uncertainty and improving the input that is required for the structural design of these concepts.
Preliminary Hazard Analysis of the Activities of Inspection and Repair in a Cargo Tank of an Operating FPSO
Authors: Van Loon Karoline De Carli Loureiro , Orsolini Ana Luisa , Ysla Karla , Martins Marcelo Ramos 
Published: October 2015

The number of Floating Production Storage and Offloading units (FPSOs) operating worldwide has been increasing due to the fact that they are well recognized as one of the most economical systems to develop offshore (ultra) deep water areas lacking infrastructure. In order to comply with the regulations, especially the Classification Society rules, and to monitor the hull integrity, all the cargo tanks must be submitted to periodical surveys on a continuous base. Eventually during this survey, some anomalies may be found, such as cracks and thickness loss in structural elements that will require repairs.
This study provides a brief review of the methodology provided by the Guidelines for Formal Safety Assessment (FSA) proposed by IMO (2002) and its application to the activities performed to survey and repair a cargo tank of an operating FPSO. A detailed description of these activities is provided in order to define the scope and frontiers of this study. Special attention is paid to the first step of the FSA methodology and the “Preliminary Hazard Analysis” technique is applied to the mentioned activities.
Gas Filled Pipelines Monitoring Using Multipoint Vibroacoustic Sensing
Authors: Bernasconi Giancarlo , Giunta Giuseppe , Chiappa Fabio 
Published: October 2015

eni S.p.A. has promoted and supported a research project (DIONISIO) for the design of a proprietary pipeline monitoring system, exploiting negative pressure waves and statistical analysis principles. A discrete network of pressure and vibration sensors are installed on the pipeline, at relative distances of tens of kilometers. The acoustic and elastic waves produced by third party interference and by flow variations (leaks, spills, valve regulations, pig operations, etc.), propagate along the pipeline, and they are recorded at the monitoring stations. Multichannel processing of the collected signals enables the real time detection, localization and classification of the triggering event.
The system has been tested in single phase and multiphase transportation lines during several field campaigns. This paper collects the results for gas transportation pipelines.
The field experience has been used to upgrade the prototypal version of the system to an industrial version, that is currently operative, or in an advanced installation phase, on several pipelines in Italy and in Nigeria, and it has detected tens of bunkering activities with a localization accuracy of about 25 m, from a distance up to 35 km from the sensing point.
Flexible Pipe Hysteretic Bending Behavior: Comparison With Experimental Characterization and Finite Element Method
Authors: Péronne Simon , Izarn Cécile , Estrier Pascal , Caro Olivier , Leroy Jean-Marc , Charliac David 
Published: October 2015

The flexible riser global behavior is of major importance during the design phase of a flexible riser system configuration.
Flexible riser design is an optimization loop involving several iterations. The flexible riser main mechanical characteristics are used as inputs into the global dynamic analysis. The dynamic analysis is performed to derive global loads that are then used for the flexible riser design. At each step of the riser design optimization loop, from the global configuration to flexible pipe cross-section, accurate knowledge of the flexible pipe mechanical characteristics is essential.
One of the main mechanical characteristics of a flexible riser that drives its global behavior is its bending stiffness. Considering the flexible riser composition, the bending stiffness is much lower than its torsional and axial stiffnesses and therefore has a larger influence on its static and dynamic behavior.
In order to simplify the global analysis, the first approach considered uses a linear bending stiffness. In this case, only the contribution of the polymer layers of the flexible is accounted for. The linear bending stiffness is therefore only impacted by thermal loads.
In reality, because of the friction that can occur between the armor layers, the bending behavior is non-linear and the relation between bending moment versus curvature is hysteretic. This hysteretic behavior induces energy dissipation and therefore, when accounted in the global modeling of the riser, reduces the curvature response of the flexible riser.
Technip and IFPEN previously developed a model to describe mechanical flexible pipe characteristics. This model is based on the finite difference method. To ensure the accuracy of stress prediction of this method in response to external loads (tension, curvature, internal pressure and external pressure), results are validated with both experimental and finite element methods.
This paper presents the theory of bending behavior of a flexible riser and explains how the model is used to derive a hysteric bending model. The matrix of experimental tests campaigns performed on flexible pipe to characterize bending behavior of flexible risers, and comparisons with hysteretic behavior predictions from the FEA and finite difference models are presented.
Finally results from experimental tests, FEA and calculated hysteretic bending models are implemented into the dynamic analysis model of a flexible riser system. Then the global behaviors of the flexible pipe configuration, with the different properties, are compared.
Stochastic Linearization of the Morison Equation Applied to an Offshore Wind Turbine
Authors: Housseine Charaf Ouled , Monroy Charles , de Hauteclocque Guillaume 
Published: October 2015

This paper aims at comparing different implementations of the Morison equation for seakeeping analysis in frequency domain. For more consistency, different wave models are considered and the total wave field (incoming wave, the diffracted and the radiated wave field) is included in the Morison equation.
A state-of-the-art of theMorison equation and the drag force linearized forms are presented. The implementation procedure, based on an iterative frequency domain scheme, is developed for the regular and the irregular wave cases.
Seakeeping analysis of an offshore wind turbine is considered as an application case. A comparison between numerical simulations and measured responses is presented.
For the floater’s numerical model, skirts damping effect and hydrodynamic loads applied on cylindrical bracings are modeled using the Morison equation. The drag and inertia coefficients are considered constant for all sea states and calibrated using the experimental results.
Response amplitude operators (RAOs) and short-termstatistics of motions show a good agreement between experimental and numerical results. The influence of different calculation parameters including the wave model (regular/irregular) and the wave fields (incident/total) are investigated.
Whitening Generation in PVDF Under Cyclic Loading
Authors: Silva Marlon Demauir Cozine , Laurentino Daniele Alves , da Costa Marysilvia Ferreira , Costa Neto Celio Albano da 
Published: October 2015

Whitening is defined as the change in the opacity of a polymeric material due to microvoid nucleation and/or grow, resulting in volume increase and possible modification of the mechanical properties. Its formation may arise from processing conditions or mechanical stresses acting in the polymers. The understanding of the whitening phenomenon and its effect on mechanical behavior is of great importance for engineering application; for instance, poly (vinylidene fluoride) (PVDF) is widely used as pressure barrier in flexible raisers, where high pressure and aggressive media are presents and the presence of whitening may increase the gas permeation rate.
The present study, cyclic loading experiments were performed on PVDF to generate whitening in a controlled manner. Subsequently, the whitening effect on the mechanical properties were evaluated using tensile tests and the structure was evaluated using X-ray diffraction, while the fracture surface was analyzed via scanning electron microscopy. It was observed that cyclic load was able to nucleated the voids and there was an increase in the crystallinity and in the mechanical properties of the material.