bluuebunny/crossref_metadata_2025 huggingface dataset:
Review and Comparison of Collated Offshore Mooring Chain Fatigue Test Data
Authors: Farrow Gary H. , Potts Andrew E. , Jal Eric , D’Arcy Evans Nicholas , Kilner Andrew A.
Published: November 2019

The first phase of the Chain FEARS (Finite Element Analysis of Residual Strength) Joint Industry Project (JIP) aimed to develop guidance for the determination of a rational discard criteria for mooring chains subject to severe pitting corrosion which, based on current code requirements, would otherwise require immediate removal and replacement. Critical to the ability to evaluate the residual fatigue life of a degraded chain, is to have an accurate estimate of the chain in its as-new condition, thereby providing a benchmark for any loss in fatigue life associated with severe corrosion or wear.

A large collection of fatigue test data was collated for comparison and to establish underlying trends in as-new mooring chain fatigue response, and a non-linear multi-axial Finite Element Analysis (FEA) fatigue assessment method was developed to correlate against available as-new chain link fatigue test data and underlying failure trends [1,2] as part of the JIP achieving this critical requirement.

This study sought through collation and review of available fatigue test data to:

• Identify relationships between chain fatigue performance and the key input parameters of chain type, grade and environmental conditions.

• Compare and validate the fatigue test data against the current Code formulations for chain fatigue endurance.

• Determine chain nominal stress S-N fatigue endurance curves against which to validate a numerical model developed as part of the Chain FEARS JIP for the assessment of as-new chain link fatigue endurance.

The collated fatigue data was separated into groups associated with offshore mooring chain type (i.e. stud and studless), grade (i.e. ORQ, R3, R4 and R5) and environmental conditions (i.e. free corrosion in seawater and in-air) for review.

Good correlation occurred between the two standard deviation lower bound of the mean curves and current Code formulation design curves. The mean curves of the collated fatigue test data were considered representative of the overall fatigue performance of chain links and as such formed a good basis for subsequent development and the validation of an FEA model for the assessment of chain fatigue endurance [1,2].
Development of Flexible Composite Pipe Cross-Section Design Software Based on Visual Basic
Authors: Sun Xinyu , Bai Yong , Zhao Jiannan , Liu Chang , Zhang Xiaojie
Published: November 2019

With the rapid development of science and information technology, software systems are widely used in all walks of life in society. Composite materials have become the hotspot and trend in pipe development, which greatly broaden the application field of composite pipes. Aiming at the requirement of composite pipe section design in composite flexible pipe factories in actual production, this paper simplifies the flexible composite pipe into a uniform continuous model, and develops a pipe section design software based on Visual Basic environment. According to the numerical calculation method in mechanics and the empirical formula, considering the production error and safety factor, this paper puts forward a reasonable method for designing the flexible composite pipe section, and develops a system for calculating it using Visual Basic. Based on the performance of raw materials and the requirement of customers for pipe pressure, this software can figure out the section data of steel strip pipe, steel cord pipe, polyester pipe, Kevlar pipe, and fiberglass pipe respectively, and obtain the design pressure, minimum bending radius and other parameters, thus improving the efficiency of the design process. At the same time, raw material quotation and pipe cost price can be calculated to facilitate the purchase of raw materials, pipe storage and sales. This software is an ideal tool for calculating flexible composite pipe cross-section data.
A Novel Semi-Submersible Floating Wind Turbine Platform Design Based on Tuned Liquid Column Dampers
Authors: Mao Baijin , Sun Jili , Tang Zecheng , Feng Bo , Zhang Weijie , Zhang Dahai , Si Yulin
Published: November 2019

Floating offshore wind turbine (FOWT) has been a hot research topic in recent years due to its great potential in deep sea wind energy harvesting. However, the floating platforms will introduce additional degrees of freedom to the system, which results in much more ultimate and fatigue loads onto the wind turbine structure compared with fixed bottom types. The load issue has been the major design challenge in developing FOWTs.

In this paper, we report a novel semi-submersible supporting platform design, named MUsupport, aiming to improve the dynamic responses and reduce loads for FOWTs. The proposed semi-submersible MUsupport is mainly composed of one main column attached to the tower and four offset columns. Particularly, instead of simply filled with ballast water, the four columns act as four tuned liquid column dampers (TLCDs), and the oscillating liquid inside the TLCDs is supposed to help improve the dynamic responses of the semi-submersible platform, thus reducing the loads. The sizing of these TLCDs are determined by frequency analysis, and the detailed structural properties for MUsupport are described in this paper. Additionally, in order to better study the damping effects of the TLCDs, the dynamic model of MUsupport FOWT in the pitch-surge-heave plane is derived based on the Lagrangian approach, and free decay simulation test is performed. It can be observed from the results that the introduction of TLCDs will bring more damping to the system dynamics, which is helpful for FOWT load reduction. Note that this is only preliminary study, and future works will comprehensively investigate its hydrodynamic and mooring behaviors of MUsupport, and aero-hydro-servo-elastic numerical simulations or experimental tests should be performed to further verify its effectiveness.
CFD Simulations of Breaking Stokes Waves
Authors: Hino Takanori , Ikenoue Harushi , Takagi Youhei
Published: November 2019

Free surface flow simulations using CFD (Computational Fluid Dynamics) can be categorized into two approaches in terms of free surface modeling. One is a two-phase flow model which solves both water and air. The other is a single-phase approach in which only the water region is solved with free surface boundary conditions. Breaking waves have been simulated by many researchers using CFD techniques with two-phase flow models in the most cases. In ship flow CFD applications, however, a single-phase approach is often used since this is considered to be more effective and efficient. However, when a single-phase method is applied to flows with bow wave breaking of a blunt ship, it is observed in some cases that numerical solutions fail to reproduce wave breaking well. This may be due to the differences of the air-water interface treatment between two-phase and single-phase approaches. To investigate these differences, breaking of Stokes waves is simulated by using both single-phase and two-phase flow models. The comparisons of single-phase and two-phase approaches are made in wave profiles, pressure and vorticity distributions. The velocity distributions near the free surface boundaries are also compared. Through these comparisons, impact of free surface boundary conditions in a single-phase approach to wave breaking phenomena is discussed.
CFD Analysis on Similarity Criteria of Hydrodynamic Characteristics for Gravity-Installed Anchors
Authors: Gao Jiancai , Liu Haixiao
Published: November 2019

For reduced-scale model tests of gravity-installed anchors (GIAs), it is of great significance to extrapolate the testing results to prototype. This highlights the necessity of investigation of similarity criteria. The present work aims to find the similarity criteria of three prioritized hydrodynamic characteristics including VT, HP, and Cd for GIAs during installation in water through CFD simulations. In the present study, free falling processes of different reduced-scale T98 anchor models and prototype anchor is simulated, from which VT, HP, and Cd are extracted and analyzed to get the fitting curves for these three characteristics over reduced-scale λ. Based on these curves, hydrodynamic characteristics for prototype and other reduced-scale model can be extrapolated from model testing results. And, the researching procedure in this paper sets an example and reference to study about similarity criteria for other hydrodynamic characteristics.
The Design and Installation of Wet Park Configuration for Dynamic Umbilicals in Ultra-Deep Environment
Authors: Reagan Perdinan , Lovie Graeme
Published: November 2019

Two dynamic umbilicals in a tethered lazy wave configuration were required to be wet parked in an ultra-deep environment with a water depth in excess of 2900m.

The close proximity to the pre-installed mooring lines, along with the in-place configuration requirements (seabed connection location, short seabed tether length, quantity of distribution buoyancy modules) made the design of a viable wet park configuration particularly challenging.

Strong current was also a major driving factor. The speed and dominant directionality influences the umbilical hump excursion, the stability of the umbilical and potential interference between the umbilicals and mooring lines. Several different routes were assessed to overcome the key problems as part of the wet park engineering solutions.

The installation of these umbilicals into their wet park configurations similarly presents a significant engineering undertaking.

An innovative and unconventional solution was chosen for the design of the wet park. The configuration utilises an umbilical ‘cross-over’, which allowed both umbilicals to be laid perpendicular to the dominant current direction and clear of any interference risks. An installation methodology was developed to successfully hook up the tether and lay down the umbilicals. Custom components and installation aids were designed for this purpose.
An Experimental and Numerical Study of Added Mass and Damping for Side by Side Plates in Oscillating Flow
Authors: Solaas Frøydis , Mentzoni Fredrik , Abrahamsen-Prsic Mia , Kristiansen Trygve
Published: November 2019

Forced harmonic oscillations of seven configurations consisting of horizontal side by side plate elements are performed experimentally and numerically. The configurations are oscillated in vertical direction and represent generalized mudmats of subsea structures. The tests are performed for Keulegan-Carpenter (KC) numbers relevant for force estimation during lifting operations. Hydrodynamic added mass and damping coefficients are presented. The coefficients are found to be amplitude dependent for all configurations tested. The interaction effects between the plates increase with increasing amplitude and decreasing distance between the plates. For oscillation amplitudes small compared with the gap between the plates, the plates behave approximately like individual plates. A study of the relation between the damping force and the added mass force for the tested structures illustrates the importance of applying representative damping coefficients in numerical analysis of marine operations.

Numerical results are obtained using a potential flow solver (BEM) and a viscous flow solver (CFD). Low-KC added mass coefficients predicted with the BEM are in accordance with the experiments. There is acceptable agreement between the CFD and the experiments. Best agreement is obtained for small KC numbers. For increasing KC numbers, the differences are, in general, larger. This is possibly due to the CFD being based on two-dimensional laminar flow.
Bore Pressure on Horizontal and Vertical Surfaces
Authors: Liu Jiaqi , Hayatdavoodi Masoud , Ertekin R. Cengiz
Published: November 2019

Bores generated by dam-break and initial mound of water and their propagation over horizontal and inclined surfaces are studied by use of theoretical approaches. Calculations are carried out in two and three dimensions and particular attention is given to the bore impact on horizontal and vertical surfaces. Downstream of the initial mound of water may be wet or dry. Discussion is provided on the influence of the downstream water on the bore behaviour and impact. Three methods are used in this study, namely the Reynolds-Averaged Navier-Stokes equations (RANS), the Green-Naghdi (GN) equations and Saint Venant equations (SV). The governing equations subject to appropriate boundary conditions are solved with various numerical techniques. Results of these models are compared with each other, and with laboratory experiments when available. Discussion is given on the limitations and applicability of these models to study the bore generation, propagation and pressure on horizontal and vertical surfaces. It is found that the GN equations compare well with the RANS equations, while the SV equations have substantially simplified the solution.
Effective Harmonic Analysis With Spectrum Filtering Technique
Authors: Peng Zhong , Grant Hazel , Sproson Richard
Published: November 2019

A spectrum filtering technique has been introduced to improve harmonic analysis in this study. The impact of site characterization and physical processes have been examined to justify the necessity of applying the spectrum filtering technique following classic harmonic analysis. Investigations show that the imperfection of the harmonic toolbox, e.g. T_Tide, could be attributed to significant contributions to the long period energy of density gradient and background currents, the greater variability of current amplitude energy, and the larger energy surrounding the clustering diurnal and semi-diurnal tidal constituents. From applications on hydrodynamic model data, this study supports the argument that harmonic analysis with the spectrum filtering technique could significantly improve the accuracy of tidal energy and residuals separation.
Numerical Investigation on the Rogue Wave Occurrence in Crossing Wave Fields
Authors: Liu Shuai , Zhang Xinshu , Song Xingyu , Chen Ke
Published: November 2019

A series of directly numerical simulations of potential Euler equation have been performed using high-order spectral (HOS) method, to investigate the nonlinear wave statistics and the probability of rogue wave occurrence in crossing sea states. Several typical crossing sea states in deep water with different wave steepness are chosen for the computations. The ensemble statistical properties for those crossing waves are measured, including the temporal evolution of directional and omnidirectional wave spectra, exceedance probability of wave crest amplitude, as well as the kurtosis and skewness of free surface elevations. Particular attention is paid to the correlation between kurtosis and rogue wave occurrence. Our numerical results suggest that the global wave steepness plays a significant role in the statistical properties of crossing seas. Results also show the dependence of rogue wave occurrence probability on the kurtosis of free surface elevations.
Numerical Methods for Interlink Stiffness Formulations and Parameters Sensitivity of Out-of-Plane Bending in Mooring Chains
Authors: Edward Ceasar , Dev Arun Kr.
Published: November 2019

Mooring components used for offshore floaters are conventionally designed only to resist axial loads with minimum resistance to bending loads. However, the unprecedented failure of four mooring lines of the Girassol Buoy followed by new modifications of similar buoys exposed the gaps in the existing methodology for failure assessment. The root cause of this failure was attributed to the critical role of out-of-plane (OPB) bending induced fatigue which reduced the fatigue life by 95%. The methodology to incorporate OPB fatigue for failure assessments involves a complex process due to numerous parameters required in the formulations and variability of mooring configurations. One of the most critical steps required to simplify methodology is the formulation of the interlink stiffness, contact stiffness and global stiffness of the chain segment. Currently, the interlink stiffness is derived from full-scale laboratory testing which is expensive and has limitations in generating data for a range of configurations.

This paper focuses on producing the interlink stiffness using numerical simulations based on non-linear FE analysis to capture the complex interlink contacts mechanism at the mating surface, elastic-plastic material properties considering non-linear isotropic and non-linear kinematic behaviors during OPB response modes, and compare the numerical models based on available experimental data. The numerical model developed for this research are designed to replicate real case OPB scenarios which induces both rotation and vertical displacements at the mooring connection points. This is different from models studied so far that induces only vertical displacements to study OPB responses which produces conservative results.

Further to this, an exhaustive analysis of the key OPB inducing parameters like chain diameter, types, pre-tension, instantaneous tensions, proof loading, residual stress, material properties, boundary condition etc. are required for understanding the underlying failure mechanism. This research also investigates the key OPB parameters and analyze their inter-dependencies, proportionalities and relative sensitivities to understand their overall contribution to OPB failures. This paper presents the first part of this research work which focuses on some of these key aspects to generate the simplified methodology using numerical methods.

The findings of this research can be used to generate a database of interlink stiffness for application to a range of mooring configurations and develop mathematical formulations for carrying out a direct assessment of OPB fatigue in combination with tension-tension fatigue failures and proposes potential mechanisms for improving the fatigue life.
Investigation of Focused Wave Impact on Floating Platform for Offshore Floating Wind Turbine: A CFD Study
Authors: Zhou Yang , Xiao Qing , Liu Yuanchuan , Incecik Atilla , Peyrard Christophe
Published: November 2019

Most existing research related to a semi-submersible offshore floating platform focuses on the wave-structure interaction under either a regular or irregular wave condition. In order to numerically model the irregular wave impact on a semi-submersible platform hydrodynamic response with a low computational cost, in this study, a focused wave is utilized. The platform under this consideration is the DeepCwind semi-submersible platform. A high fidelity CFD numerical solver based on solving Navier-Stokes equations is adopted to estimate the dynamic response and the hydrodynamic loading of the platform. The focused wave is firstly generated based on a first order irregular wave theory in a numerical wave tank and validated against the linear wave theory results. Next, for CFD coding validation, the surface elevation of a fixed FPSO model associated with a focused wave is calculated and compared with the benchmark results. At last, the dynamic responses of the platform are numerically simulated under various focused wave parameters, and the results are compared with those obtained from an in-house potential flow theory tool at Électricité de France (EDF). It is found that the predicted CFD surge motion responses are close to those achieved with the second order potential theory while differ from the results obtained using linear potential theory. As to the pitch motion, differences are observed between two results, due to the different methods used for second order loads and viscous effects calculation. Turning to the results under different wave parameters, the surge and heave motion responses increase as the wave period goes up. However, the pitch motion is not affected significantly by varying wave periods. It may be due to the fact that the low-frequency effects have limited impact on the pitch motion. The strong nonlinearity at extremely large wave amplitude will be the task in our near future study.
Oscillating Water Column Motion Inside Circular Cylindrical Structures
Authors: de Oliveira Costa Daniel , Sales Junior Joel Sena , Fernandes Antonio Carlos
Published: November 2019

A non-linear mathematical model is presented for the Equation of Motion of the Water Column inside circular cylindrical structures in different cases, comparing to previous models in literature. Experimental model tests were carried out investigating the water column decay under given initial conditions, and an analysis is performed for each cycle showing the dynamic behaviour of OWC evolving in time. The results show asymmetric pattern in the time series acquired in the decay tests as a consequence of variations of the Added Length and quadratic viscous damping as the direction of the flow changes, as observed in previous studies.

A general procedure is proposed to assess the unknown parameters including the quadratic damping viscous coefficients through the concept of “equivalent linear harmonic” as a linearisation of such terms, enlightening its dependence on the motion amplitude as well as the water column draft.

Experimental data for the OWC response under a set of incoming regular waves is also presented, comparing the results to numerical simulation through a solver based on the estimation of the damping coefficients obtained in the decay tests.
Study on the Effect of Impact Load Generated From Pile Driving on Adjacent Berthing Structure
Authors: John Jeena Mary , Saha Nilanjan , Sundaravadivelu R.
Published: November 2019

The extension of ports and offshore structures has increased due to feasible marine transportation with more cargoes pouring into the ports across the world. In many ports, there is limited availability of favourable conditions to berth and lack of space for an extension. This leads to the construction of new berthing structures at very close vicinity to existing structures which are aged but significant. One prime concern in such berths is the vibration that will be transmitted to the existing old structure during the construction of the new one. Therefore there is a requirement to keep vibration effects under control to ensure that existing structures remain serviceable.

One of the scenarios that determine the intensity of vibration that will be transmitted to soil and adjacent structure is the impact load applied on the pile. In the paper, the study is chosen at a specific port which needs reconstruction and extension due to the change in nature of the cargo to be handled and its requirements and also due to deterioration of aged berthing structure. Therefore, this study aims to find out the effect of impact load that is applied on pile casing during the pile driving process, so that the adjacent structure and machinery can be kept serviceable. The structure, soil medium and pile driving process are modelled in PLAXIS 3D. A damping ratio of 5 percent is assumed for both structure and soil throughout the modelling. A parametric study is done by varying the load on the pile casing while pile driving. The study gives the response of the structure to dynamic loading and influence of load on peak particle velocity during pile driving that gives economical piling and also ensures the safety of the adjacent berthing structure.
CFD Analysis of a Captive Bullet Entry in Calm Water With and Without Turbulence
Authors: Rauffus René Bettencourt , Maximiano António , Eça Luís , Vaz Guilherme
Published: November 2019

Simulations are carried out for a simplified lifeboat drop test case, which consists of a captive axisymmetric generic lifeboat shape (bullet), that penetrates the water surface at a constant velocity and angle of attack. The quantities of interest are the body fixed longitudinal force FX, vertical force FZ, and pitch moment MYY.This case was previously used in a verification and validation exercise [1]. Here, a step forward in complexity is taken, as the previous numerical model is now supplemented with the eddy-viscosity based turbulence model k–ω SST. Both approaches are then used to simulate two different cases: Case 1 with minimal wake effects; and Case 3 with flow separation and significant wake. The results are compared with the experimental data. The numerical uncertainty is estimated for both models. It is seen that for Case 1 the difference between both models is mostly within the comparison uncertainty, except for the longitudinal force FX, where the turbulent flow predicts a larger force, improving the comparison with the experiments. The loads predicted with turbulent flow stayed mostly within 6 % of the laminar flow. For Case 3 small differences between both models are found during/after the wake collapse stage. However, this difference is often within the comparison uncertainty. A reasonable agreement is found with the experimental data, except for FZ after the bow wake collapse. The turbulent flow improves slightly on the laminar approach regarding the agreement with the experiments, however it can be argued if this difference justifies the increased computational cost of the turbulence model.
Subsea Spare Parts Analysis Optimisation
Authors: Coffey Tiarnan , Rai Christopher , Greene John , O’Brien Bromley Stephen
Published: November 2019

The main objective of this paper is to present a fully quantitative methodology combining reliability, availability and maintainability (RAM) analysis and cost-benefit analysis (CBA) approaches to determine the optimum sparing strategy for subsea components considering reliability data, lead times, availability and cost. This methodology can be utilized at any stage of an asset lifecycle, from design to operation and can be adjusted to reflect modifications throughout the life of field.

Using commercially available RAM analysis software, Maros [2], a reliability block diagram (RBD) is constructed to represent the reliability structure and logic of the system being analyzed. Retrievable components, for which spares would be suitable, are then identified within the model to review and update the failure modes and reliability information for each component. Reliability information can be based on project specific data or from industry-wide sources such as OREDA. The RAM analysis software uses the Monte-Carlo simulation technique to determine availability. A sensitivity analysis is then performed to determine maximum availability while holding the minimum required stock level of spare components.

A sparing priority factor (SPF) analysis is then performed in addition to the RAM sensitivity analysis to support those results and consider spare purchase, storage and preservation costs. The SPF gives a weighting to the storage cost against the potential impact on production. The SPF is a number used to determine a component’s need to have a spare. A high SPF indicates an increased requirement to hold a spare.
Fatigue of Mooring Chains Connected to Offshore Floating Structures Considering Out of Plane Bending Effects
Authors: Hellum Vidar , Ding Songxiong , Lassen Tom
Published: November 2019

Reliability against fatigue fracture is an issue of major concern in the design of offshore mooring systems with chain segments. The present paper describes the investigation of the effect of OPB (out of plane bending) and IPB (in plane bending) loading modes on the fatigue performance of chain links in critical positions. The hang-off design at the floater is based on long rods with bearings at the connection points to the floating structure. The purpose of the paper is to shed some light on possible design improvements on the connection design when using the available design guidelines for calculation of combined Tension-Bending fatigue in the mooring line.

A challenge when using the existing design guidelines is that they often predict very short fatigue lives for what used to be a conventional hang-off design. A possible method for mitigating this is to improve the connection design so that the interlink angles could be reduced due to the slip in the bearings in the end of the rod. This would lower the bending stress to be occurred in those critical links. The present paper investigates the optimum length connecting rods and friction in the bearing on the fatigue lives of top mooring chains.

A case study for 125 mm mooring chain and a pretension of 1200 kN is included. A non-linear beam model established according to the BV guidelines showed good ability to model the behavior of the 125 mm chain observed during the test. It is however a challenge to select the right interlink rotational stiffness and the correct bearing friction coefficient. An optimization analyses demonstrated that a rod length should be minimum 3 meters and the friction coefficient should be down to 0.15.
A Fundamental Study on Tsunami Protection Measures for a Vessel Moored at a Wharf Considering the Backwash Influence
Authors: Masuda Mitsuhiro , Minami Kiyokazu , Masuda Koichi
Published: November 2019

When a tsunami attacks in harbors, a vessel moored at a wharf is occurred a serious damage. The first wave of the tsunami has two forms and those are called the leading wave and the backwash. And, it is difficult to predict the form of the first wave of tsunamis. Authors have been studying about damage protection measures against the leading wave of vessels moored at wharves. However, it is also necessary that a damage protection measure against the backwash of vessels moored at wharves is considered. In this study, it is examined the damage status of a vessel at a wharf due to the backwash. Then, it is examined the influence of the backwash to the author’s proposal tsunami protection measures. The three dimensional MPS (Moving Particle Semi-implicit) method is used. The Backwash is simulated as the dam break phenomenon. Outflow angles, flow velocities, mooring conditions and with and without of tsunami protection measures are considered.
Evaluation of the Ocean Circulation for the Solomon Sea Using the Regional Ocean Modeling System (ROMS)
Authors: Bento A. Rute , Coelho Henrique , Yang Chunxue
Published: November 2019

The Regional Ocean Modeling System (ROMS) is a free-surface, terrain-following, primitive equations ocean model and it was implemented to perform a high-resolution 10-year hindcast study of Solomon’s Sea circulation patterns. The model was executed with a resolution of 1/36°, initial conditions from HYCOM+NCODA Global 1/12° and was forced by CFSR/CFSV2 momentum, mass and heat fluxes. The model was validated by comparing the simulated temperatures, salinities and flow patterns with satellite data, Argo floats and Ship ADCP measurements. In general, the model captured the main circulation patterns and performed well for the Solomon Sea. The modelled Temperature and Salinity profiles were comparable with the observations, with some error variability in the thermocline layer, which agreed with previous studies.
Corrosion Behaviour of Cupronickel 90/10 Alloys in Arabian Sea Conditions and its Effect on Maintenance of Marine Structures
Authors: Abbas Muntazir , Shafiee Mahmood , Simms Nigel
Published: November 2019

The composition of seawater plays a very significant role in determining the severity of corrosion process in marine assets. The influential contributors to the general and pitting corrosions in marine structures include temperature, dissolved oxygen (DO), salinity, PH, chlorides, pollutants, nutrients, and microbiological activities in seawater. The Cu-Ni (90/10) alloy is increasingly used in marine applications such as heat exchangers and marine pipelines because of its excellent corrosion resistant properties. Despite the significant advancements in corrosion shielding procedures, complete stoppage of corrosion induced metal loss, especially under rugged marine environments, is practically impossible. The selection of appropriate metal thickness is merely a multifaceted decision because of the high variability in operating conditions and associated corrosion rate in various seawater bodies across the globe. The present research study aims to analyze the early phase of corrosion behavior of Cu-Ni (90/10) alloy in open-sea conditions as well as in pollutant-rich coastal waters of the Arabian Sea. Test samples were placed under natural climatic conditions of selected sites, followed by the mass loss and corrosion rate evaluation. The corrosion rate in the pollutant-rich coastal waters was around five times higher than in the natural seawater. A case study on marine condenser (fitted with of Cu-Ni 90/10 alloy tubes) is presented, and a risk-based inspection (RBI) plan is developed to facilitate equipment designers, operators, and maintainers to consider the implications of warm and polluted seawater on equipment reliability, service life, and subsequent health inspection/ maintenance.
Impact of High Order Wave Loads on a 10 MW Tension-Leg Platform Floating Wind Turbine at Different Tendon Inclination Angles
Authors: Milano Daniel , Peyrard Christophe , Capaldo Matteo , Ingram David , Xiao Qing , Johanning Lars
Published: November 2019

Floating wind technology is being developed rapidly with the aim of harvesting high-energy wind resources in medium and deep water areas, unreachable using fixed bottom solutions. Given the complexity of these systems, the interactions between the structure and incident hydro-aerodynamic forces need to be well understood. While numerous solutions are being explored, an optimal design is yet to be established within the industry.

This study explores the effects of tendon inclination on the dynamic behaviour of a 10MW tension-leg platform (TLP) floating offshore wind turbine (FOWT), and the interaction of different design solutions with higher-order hydrodynamic loading. The model was subject to an extreme sea state in order to capture second and third-order wave effects, and the nonlinear waves were generated via the high-order spectral (HOS) method. The analysis was performed using the hydrodynamic engineering tool CALHYPSO, in-house developed by EDF Lab.

Second and third order inertial hydrodynamic loads were included in the time-domain simulations in order to capture low frequency loads and ringing effects respectively. Results show that difference-frequency second order effects have a negligible impact on motions and tendon tensions of the analysed floating wind turbine model, while third order terms can significantly enhance the dynamic response of the system to extreme incident waves. While inclined-leg floater configurations presented improved motion and tendon tension responses under linear loading, the inclusion of quadratic and triple-frequency contributions showed that tendon inclination can in fact increase tension variations in the mooring lines when subject to extreme wave climates. This can lead to slacking in the mooring lines being observed more frequently in inclined-leg configurations. The results therefore suggest that neglecting third order effects, as commonly done in industry, can lead to significant underestimations of motion and tendon tension responses of tension-leg platform wind turbines.
Experimental Assessment of Vertical Shear Force and Bending Moment in Severe Sea Conditions
Authors: Horel Boris , Bouscasse Benjamin , Merrien Arnaud , de Hauteclocque Guillaume
Published: November 2019

Recent studies have benchmarked the prediction of wave vertical bending moment (VBM) of ship in waves [1][2], and found significant scatter among the numerical codes.

Unfortunately, experimental data in extreme waves, that are relevant to ship design, are not often easily accessible, nor completely fitted to rigorous comparison to numerical codes. Then, the improvement of numerical tools and the modelling of ship’s internal loads still requires accurate experimental data measured in steep waves (ratio wave height H to wavelength λ, H/λ = 0.1) where the ship behavior and loads are modified by non-linearities.

Thus, in order to validate simulation codes, which underlies rules requirement, and to establish criteria that makes ships safer to sail in severe sea conditions, experiments are carried out in the 50m × 30m × 5m hydrodynamic and ocean engineering tank of Ecole Centrale Nantes. A 1/65th scaled model of a 6750-TEU containership is used. The ship is moored and several combinations of wavelength and wave height are tested.

While segmented hulls are commonly instrumented with strain gauges, the present experiments are performed on a segmented hull with a 6DOF sensor located close to the amidship. This setting allows for a very stiff model which dramatically reduces the hydroelastic effects. According to previous study [1], the position of the sensor is chosen where the bending moment is supposed to reach a maximum value. The model motion is measured through a Qualisys IR tracking system and accelerometers are located on the fore and aft of the beam.

Also, each of the 9 segments is equipped with a 3DOF dynamometer to measure the hydrodynamic loads on the hull. This allows for recovering the hydrodynamic loads on the segments and then to compute the shear force and bending moment discretized all over the ship length. A comparison is therefore possible with the 6DOF sensor. Details of the computations are given in the paper.

A particular attention is paid to the reproducibility and repeatability of the tests. The innovative experimental setup and the measured data are presented in the paper. Based on previous studies [3], the effects of the non-linearities are also discussed.
Understanding the Capability of RANS Based Turbulence Models on Fully Turbulent Channel Flow
Authors: İlter Yasin Kaan , Ünal Uğur Oral
Published: November 2019

Fully turbulent channel flow is a very common and effective way to investigate the boundary layer flow over the flat plates. Mean flow characteristics of the channel flow can be predicted using steady Reynolds Averaged Navier-Stokes (RANS) simulations although the turbulent flow has an unsteady nature. The objective of the present study is to evaluate the predictive capability of the turbulence models, which are based on RANS decomposition, in channel flow involving smooth surfaces. The study covers the application of the Reynolds-stress based second-moment turbulence closure model and the most preferred linear eddy viscosity models to determine the mean flow characteristics. The turbulence properties were compared with the DNS data obtained from the open literature. Also, an iterative study was performed for the fine-tuning of the coefficients appearing in the Reynolds-stress turbulence model. A tuned version of the Reynolds-stress model for two different frictional Reynolds numbers (Reτ) of 180 and 590 is presented. These studies will form a basis for further computations on the channel flow with a higher Reynolds number range and different channel sections. They will also serve as the initial steps for the future experimental and computational studies that will focus on the understanding of the flow mechanism over the dimpled surfaces at Reynolds numbers (based on half channel height and mean bulk velocity) up to 2.105.
Estimating Second Order Wave Drift Forces and Moments for Calculating DP Capability Plots
Authors: Barzegar Valikchali Saeed , Anderson Mitchell , Molyneux David , Steinke Dean
Published: November 2019

The DP capability plot is a useful tool to show the limitations of a dynamic positioning system for ships or offshore structures under loading from wind, waves and ocean currents. At the preliminary design stage, it is desirable to use fast methods for calculating the forces and moments caused by the environment, preferably without the need for CFD simulations or model experiments. Empirical methods are available for predicting aerodynamic forces and moments, and hydrodynamic forces and moments from currents, but little is published for second order wave drift forces. Wave drift forces and moment calculations have been carried out using WAMIT, for a series of ship hulls from OSVs to VLCCs and the effects of wave direction and frequency on the Surge, Sway, and Yaw forces and moment have been studied. The presentation of the results allows the user to interpolate the resulting drift forces and moments as a function of wave direction for a given ship size. In terms of wave drift loads calculation, it is found that the very large vessels are dominant in the low frequency waves, while smaller size ships are in high frequencies. The wave frequency and direction in which maximum drift load occurs depends on the ship size.
A Sensitivity Study for Operational Availability of Offshore Wind Energy Assets
Authors: Chiachío-Ruano Juan , Hermile Mahé , Kolios Athanasios
Published: November 2019

The rampant growth of offshore wind energy in Europe and overseas is calling for advanced operation and maintenance simulation tools for optimal infrastructure asset management. The operational downtimes due to random failures, repair times or adverse weather conditions, greatly reduce the availability of the wind farm and therefore increase the Levelised Cost of Energy of this important source of renewable energy. This paper presents a sensitivity analysis to explore the factors influencing the most the operational availability of an offshore wind farm over a particular geographical area. The analysis is carried out using a newly developed open-access tool for operation and maintenance simulation named as “OpenO&M”. The failure rates of wind turbine components and the weather safety allowable limits for maintenance vessels emerge as critical parameters for wind farm availability, specially in remote areas.
Performance of a Two-Phase Flow Solver for the Simulation of Breaking Waves
Authors: Jin Qiu , Hudson Dominic , Temarel Pandeli , Price W. Geraint
Published: November 2019

Wave breaking is one of the most violent phenomena observed in air-water interface interactions. This phenomenon commonly occurs in real ship flows and is one of the main sources of underwater noise and white-water wakes. The investigation of this phenomenon is thus important in ship and ocean engineering. The performance of a two-phase flow solver is investigated for a simulation of spilling breaking waves generated by a shallowly submerged hydrofoil (NACA0024) in a uniform flow. An algebraic Volume of Fluid (AVOF) method is applied to capture the dynamic behaviour of the free surface and a standard k-ε turbulence model is selected to capture the turbulent flow around and downstream of the hydrofoil. The wave profiles, pressure and velocity contours are computed to investigate the overall flow conditions and a detailed analysis of the flow field downstream of the hydrofoil is conducted in terms of velocity components and turbulence intensities at six measurement sections. A comparison of the numerical and experimental results shows that an accurate representation of the free surface and the turbulent flow beneath it is obtained with the present numerical scheme. It is expected that the systematic documentation of the performance of the AVOF two-phase solver will enable its more accurate and optimal use for simulating ship-related flows, as well as increase awareness of its potential shortcomings for those interested in general CFD simulation of breaking waves.
Girth Weld Joints From Long Upset Pipe Ends for Improving Fatigue Strength of Offshore Oil and Gas Pipelines
Authors: Marines-Garcia Israel , Aguilar Aarón , Aguilar Ramón , Pelcastre Mauricio , Darcis Philippe
Published: November 2019

For special high dynamic loading applications, the structural integrity of the girth welds shall withstand stress levels that might be on the limits of the permissible defect tolerances for current production welding standards for plain pipe ends. In addition, unexpected loading conditions might take the stress limits out of safe operation, which can compromise the entire line. As a solution, the cross section of the girth weld may be increased for ensuring the strength and fatigue resistance under any loading circumstances, including strain cycles of reeling installation technique. The employment of pipes with upset ends is an excellent option for those cases. To propose this option as an alternative to current offshore solution for a Major O&G company, Tenaris developed a long upset pipe end with enhanced fatigue life. The challenges of this work included the manufacturing of very long upset ends from a medium wall thickness pipe, very tight mechanical properties difference between pipe and upset material properties, and finally a welding qualification program. The improvement of the fatigue strength of this product was highly expected.

In order to achieve all requirements, especial arrangements were performed on the upsetter machine for achieving the target upset geometry; which was previously obtained by a design of experiments technique. Then the heat treatment of the pipes was designed for obtaining the tight mechanical properties difference between pipe body and upset sections. The main outcomes of the whole development are described within this paper; which include key information of how to overcome issues that might arise during the development and production stages of upsetted line pipes. The upset ends undertake a cylindrical machining; this process provides the advantage of achieving tight dimensional tolerances in the high-low girth welding alignment. The fatigue endurance data after full scale reeling experimental test are included, as well as the numerical comparison between the strain fields of plain pipe and upset girth weld unions. The welding procedure qualified during this work is described. The results of the whole development were very satisfactory and, as expected, the fatigue strength of upset ends was higher than the plain pipe.
Hybrid Model Testing of Floating Wind Turbines: Test Bench for System Identification and Performance Assessment
Authors: Arnal Vincent , Bonnefoy Félicien , Gilloteaux Jean-Christophe , Aubrun Sandrine
Published: November 2019

The present study shows preliminary results of the SOFTWIND project that aims at developing an innovative experimental test bench dedicated to floating wind turbine wave tank testing. The following methodology is based on a “software in the loop” approach that combines numerical modeling with physical modeling. The originality of the experimental approach lies in the use of an innovative set of actuators located at the top of the wind turbine tower which is in charge of emulating the response of the rotor. First, results of a sensitivity analysis on the specifications of the aerodynamic forces to be emulated are presented. Low pass filtering effect in the actuation — linked to the physical characteristics of the actuators and numerical-physical loop — are first considered through fully coupled numerical simulations for different load cases including turbulent winds, misaligned wind-wave conditions and different floaters. Then, a test bench with imposed motions has been designed for the verification of communication protocols, real-time execution for the numerical model, motion and force observers and preliminary actuator model identification. Response to rising steps combined with white noise identification of the actuator with this test bench give promising results in open loop.
Hydrodynamic Performance of a Current Energy Generator Based on WIG
Authors: Wang Jian , He Guanghua , Mo Weijie , Zhang Shijun , Man Jiangtao
Published: November 2019

The hydrodynamic performance of a novel current energy generator is studied with consideration of the effect of Wing in Ground (WIG) by Star CCM+. The pitch and heave motions of a turbine with a 2D single oscillating wing and two parallelized oscillating wings in uniform flow are simulated, and the numerical results including the lift force, drag force and moment coefficients of the hydrofoil are calculated to analyze the hydrodynamic performance of the generator. First, the convergence studies with respect to the mesh and time step are firstly carried out by compared with the published data. Secondly, the hydrodynamic performance of the WIG-based current energy extraction is investigated, and a good performance of the current energy extraction is confirmed. Finally, the effect of boundary conditions of wing and wall on the performance of the current energy generator is investigated.