bluuebunny/crossref_metadata_2025 huggingface dataset:
An Experimental and Numerical Assessment of Moss-Type LNG Carrier Seakeeping Moored to PETRONAS FLNG in Partially Filled Condition
Authors: Auburtin Erwan , Toutin Guillaume , Bin Mahmud Ahmad Fahmi
Published: September 2018

Moss-type LNG carriers (LNGC) — equipped with spherical LNG tanks — have successfully performed multiple side-by-side (SBS) offloading operations from the PETRONAS FLNG (PFLNG1) terminal since first gas in late 2016. Such LNGC are well suited for these operations as by essence their tanks mitigate the liquid impact risk, for any filling ratio.

However, regardless of the LNG tanks shape, the accurate assessment of the relative motion between PFLNG1 and a SBS-moored LNGC was critical for designing the mooring and offloading systems — in particular the LNG Marine Loading Arms (MLA) — and subsequently assessing the terminal operability.

While the issue has been extensively studied for LNGC equipped with prismatic tanks (SALT I & II JIPs [4]) and a good agreement achieved with numerical models using potential theory, literature available on coupling with LNG sloshing in spherical tanks in a SBS mooring configuration is rare. Compared with prismatic tanks, the axisymmetric tank geometry is not restricting the main sloshing modes direction: these modes are therefore free to rotate due to LNGC wave-induced motions.

An experimental wave basin model test campaign has been held at the MARIN facility to assess the behavior of a Moss-type LNGC with partially filled tanks and provide a good quality database for numerical model calibration and relative motion prediction. This carrier, equipped with Plexiglas spherical tanks, has been tested in free-standing conditions and SBS-moored to PFLNG1. A variety of loading conditions was covered for the LNGC including ballast, 20% and 50% filling. Sloshing modes have been captured with dedicated cameras and wave probes implemented in the LNGC tanks.

In this paper, the model test set-up is presented and a comparison is made between the experiments and numerical simulations, using the potential theory software Diodore™, accounting for the hydrodynamic interaction between the vessels and the coupling with the liquid motion in tanks. Particular attention is paid to the coupling effects between longitudinal and transverse motions induced by the longitudinal asymmetry, and their consequences on the design of the offloading system.
DP-Stability During Heavy Lift Operations Using a Modified Kalman Filter
Authors: Harmsen Eelco , van Dijk Radboud , Stuberg Petter
Published: September 2018

During heavy lift operations, staying on position using a Dynamic Positioning (DP) system offers many advantages compared with a mooring system. However, when the vessel is connected to another fixed or floating object during the lifting operation through its hoist wires it may experience instabilities in the DP-system. These DP-instabilities are caused by the inability of the DP system to handle the relatively stiff external spring of the hoist wire correctly. This phenomenon is well known and mitigating measures such as Heavy Lift Mode have been developed over the years that work well for stationary vessels. However, when two vessels are lifting a single object together (e.g. QUAD lift), existing solutions to prevent this DP-instability are insufficient, as the nature of such lift requires a synchronous move on DP. During studies to the fundamental behavior of a DP system during heavy lift operations it is found that modifications to the Kalman filter can prevent these DP-instabilities. Heerema Marine Contractors presented the DP-stability challenges to Kongsberg Maritime, and a joint effort resulted in an implementation of a modified Kalman filter in the Kongsberg Maritime DP system. Also a dedicated engineering analysis to predict risk of DP-instabilities for specific lift configurations has been developed. The modified DP-system is tested in large number of simulations (both desktop and a full mission simulator) to test the ability of the updated DP-system to deal with a wide range of specific heavy lift conditions. Results were evaluated between Heerema office, Kongsberg and offshore personnel for developing the optimum Kalman filter parameters. Finally, the system is tested during a dedicated DP-trial program onboard Thialf. As the results of all these tests were very successful, the new High Kalman filter was made available onboard Thialf as a permanent option next to the original functionalities. The paper addresses the steps followed to define the new Kalman filter settings, the simulations performed to test the new filter as well as to show results of the offshore tests that were done to validate the numerical analysis.
All Around Approach for the Design of a New Escort Tug Family
Authors: Figari Massimo , Martinelli Luca , Viviani Michele , Villa Diego , Enoizi Lucia , Piaggio Benedetto
Published: September 2018

The aim of the paper is to describe an industrial-academic collaboration whose main goal is the design of a new escort tug family characterized by high intact/damage stability margins, good maneuvering capability and stable behavior during escort indirect assistance.

The project addresses three main research areas: hydrodynamic design of the hull with escort capability, simulation of the escort capabilities in different operational scenario, development of control logics that will allow autonomous or unmanned operations.

The paper describes the methodological approach adopted for the design and will show some preliminary results.

The results refer to the first part of the project. CFD calculations and towing tank tests have been performed onto a prototype tug hull in order to assess the hull design and to infer simulation models able to describe the behavior of a family of vessels. In particular, the propulsion and maneuverability aspects in escort operations are deeply investigated.

Results of the project will form the bases for the conceptual application to a remotely controlled or autonomous escort tug.
Using the Floating Body Symmetries to Speed Up the Numerical Computation of Hydrodynamics Coefficients With Nemoh
Authors: Ancellin Matthieu , Dias Frederic
Published: September 2018

The open source potential flow BEM solver Nemoh (developed at École Centrale de Nantes) is widely used today, notably for the development of wave energy converters. The use of a linear potential flow theory allows quick estimations of the hydro-dynamic properties of the device, such as its added mass or its radiation damping. Nonetheless, their computation with Nemoh can still be time consuming and could be optimized to facilitate the R&D process.

Many wave energy converter concepts present symmetric shapes: for instance rotational symmetry for point absorbers or translation invariance for cylindrical shapes. These symmetries can be exploited in the BEM solver to significantly speed up the computations. In this paper, the mathematical effect of symmetries on the BEM resolution will be discussed and some results of its implementation in Nemoh will be presented.
Model Test With a Vertical Pipe to Elevate Cold Sea Water
Authors: Trigo C. C. O. , Morooka C. K.
Published: September 2018

Vertical pipes are extensively applied on offshore petroleum operations, such as subsea wellbore drilling, wellbore re-entry, installations of equipment on the sea bottom, hydrocarbon production as the conductor for oil and gas from the wellhead at the sea bottom, among other applications. Recent oil and gas field discoveries in ultra deepwater brought an increase of the amount of produced and processed petroleum onboard of floating production system. Consequently, the process plant demands more cooling capacity. One of the alternatives is to elevate cold sea water.

The present study aims to improve the understanding of the behavior of a vertical pipe forced to move at its upper end in a water tank. Displacements along the pipe length are measured, and main features of the behavior of the pipe model with its bottom end free are observed. Motions imposed at the vertical pipe intent to represent motions of the surface from the floating platform or ship, due to waves, currents and wind. Pipe model vibrations are analyzed, and results allowed improvements for the input in numerical model simulations to Orcaflex software. Developments of the analysis procedure and evaluations of the experiment allow more reliable design of riser operations with its bottom end free in actual sea operations.

In the present work, a physical model with a pipe of small diameter has been developed for the laboratory experiment, and an optical measurement system is used to measure the pipe model displacement in the water tank. Motions are imposed at the top termination by a mechanical device. Experiment is described in details and comparative analyses between experiment and numerical simulations were carried out. Results from numerical simulations as well as from the experiment brought important contributions for description and understanding of the vertical pipe behavior.
Experimental and Numerical Characterization of the Stress-Strain Behavior of Weak Sandstone Formations for Sanding Assessment
Authors: González Molano Nubia Aurora , Vila Jacobo Canal , González Pérez Héctor , Alvarellos Iglesias José , Lakshmikantha M. R.
Published: September 2018

In this study an extensive experimental program has been carried out in order to characterize the mechanical behavior of two weak sandstone formations of an offshore field for application to sand production modeling. The experimental tests included Scratch tests, Triaxial tests and Advanced thick wall cylinder tests (ATWC) where the sand production initiation and the cumulative sand produced were registered.

Numerical simulations of experimental tests were then performed using an advanced elasto-plastic constitutive model. Triaxial tests simulations allowed calibrating the constitutive model parameters. These parameters were employed for the numerical simulation of the ATWC in order to determine the equivalent plastic strain threshold required to the onset of sand production observed in laboratory for sanding assessment.

Results obtained highlight the importance to use a realistic representation of the rock behavior focusing on post-yield behavior in order to build confidence in model predictions.
Enhanced Integrity Management by Integrated Erosion-Corrosion and Fluid-Dynamic Calculations in Oil and Gas Systems
Authors: Rodríguez Bustamante J. , Gómez-Álvarez S. , Riquelme-Oliveira J. A. , Sanz-Sanz P. , Lema-Zúñiga R. F. , Mercado-Hurtado L. E. , Merino-García D.
Published: September 2018

Production system integrity in remote assets is a great challenge, conventionally addressed by the application of conservative standards, leading to costly construction materials. There is evidence that API RP14E standard, accepted as standard for erosional velocity estimations and some of the most extended carbon steel CO2 corrosion models, such as NORSOK, generally lead to conservative material loss rates, with strong impact on design and capital costs [1, 2, 3, 4, 5, 6]. Additionally, there is very little description in the literature of stainless steel CO2 corrosion models.

In this work, an approach to enhanced erosion-corrosion estimations is presented, to cover this gap in material selection. Conventional approaches are incomplete, as they disregard an accurate fluid definition, geometry, flow regimes, the integration of erosion-corrosion phenomena or the validation against experimental and field data. A comprehensive workflow that starts at the fluid characterization, considers the interaction between the phases, includes fluid-dynamic simulation for computation of the flow regime vs. well completion dependence, and calibrates state of art stainless steel erosion-corrosion models with dedicated lab and Calliper field data, was applied to the erosion-corrosion analysis in a gas condensate field.

The results have identified the main material loss mechanism at different points of the well completion and predicted the remaining life of the tubing in different scenarios. This approach enables a deeper insight into erosion-corrosion interaction with the fluid system and enhances the integrity management of an asset.
Numerical Study on the Geometric and Inertial Parameters for Oscillating Wave Surge Converters
Authors: Lin Chen-Chou , Chow Yi-Chih , Tzang Shiaw-Yih , Chiou Ching-Yen , Huang Yu-Yu
Published: September 2018

In this paper the three-dimensional numerical simulation is conducted for Oscillating Wave Surge Converters (OWSCs) using computational fluid dynamics (CFD) software FLOW-3D, based on the wave climate of the offshore sea in northeast Taiwan, that is, 1.5 meters of wave height and 7 seconds of the wave period. The results are compared with that using the wave energy converter simulation toolbox, WEC-Sim. The effects of the parameters, including the flap thickness, flap width, the position of the mass center, and flap density, are investigated, especially their influence of the energy capturing efficiency or the capture factor (CF). The simulation results show that, bigger flap thickness (d), smaller flap width (B), smaller flap density, and lower flap’s center of mass will result in a higher efficiency for power capture performance. Among the four parameters, the flap thickness is the most dominant parameter. From hydrodynamic respect, a larger drag force may occur at the sidewalls of the thick flap, and the shear force accelerate the pitch motion of the flap, in turn increasing the absorption efficiency. From a practical design aspect, the variation of the CF around the peak value is smoother for wider flap, which suggests a broad bandwidth in receiving various wave frequency in irregular waves.
Comparison of Fuel Consumption on a Hybrid Marine Power Plant With Low-Power Versus High-Power Engines
Authors: Wu Zhenying , Thorat Laxminarayan , Skjetne Roger
Published: September 2018

In this paper, we are comparing fuel consumption on a case study hybrid marine power plant with diesel gensets and batteries. Optimization methods are used to find an optimal operating point for the gensets, under different power demands, with regards to fuel consumption and NOx emissions. Three different power system example configurations for an offshore construction vessel are explored in this study, and the simulations are carried out to compare the resulting fuel consumption and NOx emissions for these power system configurations.
Variance of Fatigue Damage During Transportation
Authors: Yang Limin , Bøe Tormod , Falkenberg Erik , Korbijn Florus
Published: September 2018

Fatigue damage prediction of offshore structures during transportation is today commonly based on long term scatter diagram for the sea route. This gives a mean value for the expected fatigue. The deviation from the mean value may however be significant due to the large variability in metocean conditions for the typical short duration of the transport. The actual fatigue damage experienced during the voyage may therefore be much higher than predicted. Hence, it is recommended to take into account the variability of environmental conditions in the calculation of transportation fatigue.

The aim of this paper is to establish a method for estimating transportation fatigue where the fatigue damage is computed with a specified level of non-exceedance.

The fatigue damage is quantified by a measure as defined in OMAE2017 /1/. The distribution of this measure is obtained through Monte Carlo simulation of around 300 separate sea route scatter diagrams derived from hindcast data. The 90% percentile value (10% probability of exceedance) of the fatigue measure is then taken as target value and used for establishing a limited set of design fatigue sea states to be used in the structural fatigue damage calculations.
Performance-Based Analysis of Wind-Survivability for Large Offshore Jacket Platforms Subject to Hurricane
Authors: Liu Hongbing , Sun Liping , Huang Ao , Zhao Yipei , Chen Guoming
Published: September 2018

In connection with wind sensitivity for the large towering and open truss-type offshore jacket platforms subject to hurricanes, the wind-survivability of this large structure has attracted more attention. An innovative wind-survivability framework for the large offshore jacket platform is presented based on the performance-based analysis in this paper. The damage states of a large offshore jacket platform located in the South China Sea are divided into five grades DS1 ∼ DS5 under hurricanes, including intact, minor damage, moderate damage, severely damaged and collapsed, also the corresponding ultimate damage states LS1 ∼ LS4 are defined and derived. The results show that the braces yield failure on the bottom and top horns of the derrick are the main failure modes of the large jacket platform, which should be stronger reinforced to ensure their safety performances; the different ultimate damage state determination factors have a little influence on the wind-survivability envelopes of the jacket platform; the hurricane return period for the minor damage of the towering derrick is about 15 years, also the moderate damage is about 25 years, the severely damaged is about 165 years and the collapsed is about 225 years.
The Effect on Large Container Ships’ Fatigue due to Springing Loads Coupling Horizontal and Torsional Vibrations
Authors: Li Hui , Xu Huifen , Ren Huilong , Shen Xiaoxi , Wang Yubo
Published: September 2018

The issue of hydroelasticity caused by hull vibration has become an unavoidable problem in the design and verification of large ships. Driven by environmental protection and economical efficiency, the size of ships are increasingly larger, and the resulting springing and whipping response and their effects on fatigue damage has been paid more and more attention especially for ultra large container ships (ULCS). Many classification societies typically check fatigue damage caused by vertical bending when considering springing, while it needs to be emphasized that large container ships can suffer severe torsional loads compared to other large ships due to wide breath and big hatch openings. In the existing stress calculation method, the finite element analysis method obviously has a high calculation accuracy. However, there are so much work to do with FEM model established, and partially refined, operated at all sea states etc., which not only requires much time, but also higher computing equipment. Therefore, in this paper, a simplified calculation method of fatigue damage considering the effect of bending and torsion is proposed, and a 21000TEU will be calculated by this method. The wave loads on the hull structure will be estimated based on the 3D linear hydroelastic theory coupling horizontal and torsional vibration, and the stress caused by bending and torsion will be obtained respectively. Finally, the fatigue damage is calculated by spectral analysis method considering high frequency springing loads. Then the effect on large container ships’ fatigue due to bending and torsional vibration is discussed.
Modeling the Effect of Phase Change on LNG Impact With Open-Source CFD
Authors: Calderon-Sanchez Javier , Duque Daniel , Gómez-Goñi Jesus
Published: September 2018

The phenomenology of loads due to sloshing impact on tanks, such as those in Liquefied Natural Gas (LNG) carriers, is a problem that is currently far from being fully assessed.

A main particularity of LNG, among others (such as compressibility or hydroelasticity) is that it is carried at cryogenic temperatures, normally at liquid-vapor equilibrium. This implies phase changes may occur during sloshing impacts. However, phase change phenomena have normally been neglected in sloshing studies. Preliminary works from Behruzi et al. [1] and Ancellin et al. [2] show that phase change may have an effect on the maximum pressure load.

The current work aims to study phase change phenomenology in pressure impact events at cryogenic conditions by implementing a phase change model in the open-source tool Open-FOAM. Results will be compared against previous work by the authors (Calderon-Sanchez et al. [3]), which did not feature phase change.
A New Icebreaking Pattern for the Application in Numerical Simulation of Ship Performance in Level Ice
Authors: Li Fang , Kotilainen Mikko , Goerlandt Floris , Kujala Pentti
Published: September 2018

For the evaluation of ship performance in ice and ice loads on the ship hull, numerical simulation methods have been increasingly developed in recent years. In these models, the shapes of ice cusps broken from the intact ice sheet are idealized as either part of a circle or a triangle. Effects arising from the geometry of the loading area are neglected or idealized. Since the proper definition of the geometry of ice cusps is one of the key factors in numerical models, this paper introduces a new icebreaking pattern based on theoretical deviation. The finite difference method is adopted to approximate the deflection field of the wedge plate. This model takes a large set of factors as input while consuming little computation time. The outcome provides some new features compared to previous models. The results are validated using full-scale measurements of ice cusps around a ship hull, based on stereo camera recording and image processing. The validation shows that the derived method is appropriate in predicting realistic icebreaking patterns. Hence, it is plausible that its implementation in numerical models for ship performance in level ice will lead to improved prediction of the ship performance and ice loads on the hull.
Multivariate Extreme Analysis Methodology in Function of Structural Response
Authors: Pineau Hélène , Girard Françoise , Raynaud Stéphane , Prevosto Marc , Raillard Nicolas
Published: September 2018

Many approaches exist to build environmental contours, i.e. the ensemble of joint metocean parameters corresponding to a N-year return level. However, these contours may provide rather different curves according to their calculation process. In this work, the use of response meta-models is introduced for the inter-comparison of environmental contours for two application cases: the roll of a FPSO and the tension in a mooring line of a semi-submersible.

Some state-of-the-art methods available for modelling multivariate extremes are applied for two or more variables and in a directional context. Among the conditional models, joint parametric laws (such as Weibull, log-normal...), Heffernan and Tawn simulations and several copula are investigated. Two ways of contour building are considered in 2D and 3D: Inverse First Order Reliability Model (I-FORM) and physical-space Huseby contouring method.

The comparison between the resulting design points are presented for both applications. The combined wind, wave and current parameters statistics (including directions) are presented, in addition to the extreme loads obtained from the meta-models. The advantages and drawbacks of each method are reviewed. Some key findings are finally presented, pointing out the interest of a meta-model to determine the more realistic set of design points in function of the structure response of interest.
Development of a Lifting-Line-Based Method for Preliminary Propeller Design
Authors: Chreim Jose Rodolfo , Pimenta Marcos de Mattos , Dozzi Dantas Joao Lucas , Assi Gustavo R. S. , Katsuno Eduardo Tadashi
Published: September 2018

A novel formulation for marine propellers based on adaptations from wing lifting-line theory is presented; the method is capable of simulating propellers with skewed and raked blades. It also incorporates the influence of viscosity on thrust and torque from hydrofoil data through a nonlinear scheme that changes the location of the control points iteratively. Several convergence studies are conducted to verify the different aspects of the numerical implementation and the results indicate satisfactory convergence rates for Kaplan, KCA, and B-Troost propellers. It is expected that the method accurately describes thrust, torque, and efficiency under the moderately loaded propeller assumption.
CFD and Experimental Studies of Yield Power-Law Fluids in Turbulent Pipe Flow
Authors: Ihmoudah Abdalsalam , Rahman M. A. , Butt Stephen D.
Published: September 2018

The transport of Non-Newtonian fluids through pipelines and mud circulation in wellbores often occur in turbulent flow regimes. In this study, experiments and computational fluid dynamics (CFD) models are used to examine the influence of yield power law (YPL) fluid rheological properties on pressure loss in the flow loop in turbulent flow. Three Non-Newtonian fluids at different concentrations of Xanthan gum solutions (0.05%, 0.10% and 0.15%, by weight) are studied at flow rates ranging between 400 and 800 L/min. A fully instrumented flow loop system was used, consisting of three main sections of different inclinations: 5 m long horizontal, 5 m vertical, and 3 m inclined 45° test section. Additionally, CFD codes of ANSYS CFX 17.2 are examined and compared to experimental results. These models are based on the Reynolds Averaged Navier-Stokes (RANS) equations. The comparison is done with the results of these investigations, based on vertical and horizontal pipe frictional pressure drops. The results show that the gap between experimental and CFD models has been increased in comparison with increase concentration Xanthan gum solution at the same density of fluids. Specifically, pressure loss rises with rises in the consistency index, k and flow behaviour index, However, rises in yield stress τ0 showed less impacts on frictional pressure losses. Given these simulation outcomes, it is clear that pressure drop in the Non-Newtonian fluid in one phase flow can be more accurately predicted by used the Reynolds-Stress Models (RSM) more than Eddy-viscosity models.
Discussions on the Convergence of the Seakeeping Simulations Based on the Panel Methods
Authors: Martić Ivana , Degiuli Nastia , Malenica Šime , Farkas Andrea
Published: September 2018

Numerical problems related to the convergence of the classical panel methods which are employed for the diffraction-radiation simulations are discussed. It is well known that, for the panel methods, the convergence issues are not exclusively related to the physical parameters (wave length, body shape, draught ...) but also to the one purely numerical phenomenon which occurs when the Boundary Integral Equation Method (BIEM) based on the use of Kelvin (wave) type Green’s function is used. Indeed, due to the fact that the Green’s function satisfies the free surface condition in the whole fluid domain below z = 0, the numerical solution is polluted, at some particular frequencies, by the solution of the unphysical problem inside the body. This phenomenon which is purely numerical, is known as the problem of irregular frequencies. From practical point of view, it is not always easy to distinguish if the irregularities in the final solution are coming, from the body mesh which is not fine enough, from the physical resonance of the system, from the problem of irregular frequencies or from something else!? In this paper the authors discuss these issues in the context of the evaluation of the seakeeping behavior of one typical FPSO (Floating Production Storage and Offloading). Both the linear (first order) as well as the second order quantities are of concern and the different methods for the elimination of the irregular frequencies are discussed. Special attention is given to the calculations of the different physical quantities at very high frequencies.

The numerical tool used within this research is the Bureau Veritas numerical code HYDROSTAR which is based on the panel method with singularities of constant strength.
Experimental and Numerical Study of the Free Surface Elevation Over the Pontoons of a Semisubmersible Platform in Waves
Authors: Pessoa João , Stansberg Carl Trygve , Fonseca Nuno , Laranjinha Manuel
Published: September 2018

The region over the pontoons, especially in the vicinity of columns, is typically a critical area in terms of upwell when analyzing the air gap of semisubmersible platforms. There is indication that numerical computations using potential flow theory may in some cases overestimate the free surface elevation in this region. To assess the possibility, experimental data is compared to numerical computations in three locations under the deck box: one location over the pontoons, one location in the vicinity of the pontoons and one location between the pontoons. The data was acquired in FORCE’s towing tank facility, in Lyngby, Denmark, by relative wave gauges fixed to the moored semisubmersible platform. The experimental data is treated in order to remove the global motions from the upwell signal. The resulting free surface elevation, which includes contributions from incident, diffracted and radiated wave fields, is compared to the disturbed free surface elevation calculated with linear diffraction-radiation theory.

The study is initially conducted in irregular waves, where simulation statistics in 4 different sea states are compared to the experiments and the observed nonlinear effects are discussed. The extreme crest heights are compared with non-Gaussian models as defined in DNVGL-OTG-13 and as defined by Stansberg (2014). The study is then extended to regular waves. In a first stage we estimate the first harmonic components by removing all higher order effects, and compare the results to linear theory. For these band-pass filtered signals it is shown that results calculated with linear theory tend to overestimate free surface elevation in the location over the pontoons, but seem to correlate well with the experiments in the other locations. In a second stage the experimental crest heights are compared with non-linear models as defined in DNVGL-OTG-13 and as defined by Stansberg (2014).

It is shown in this case study that the maximum free surface elevation over the pontoons in front of upwave columns can be severely overestimated if calculated with the current state of the art numerical models, which are based on linear diffraction-radiation theory. We explain the observed discrepancy in this case primarily by a very high linear predicted amplification induced by the shallow pontoon, with resulting high local steepness leading to local breaking and dissipation. Therefore, such pontoon effects should be addressed in semisubmersible platform air-gap analysis. The work also highlights the importance of having good experimental data available when preforming such analysis.
Assessment of Current Offshore Supply Vessel Capabilities for Crew Transfer Operations in the Flemish Pass
Authors: Anderson Mitchell , Molyneux David
Published: September 2018

The Flemish Pass is a region off the coast of the province of Newfoundland and Labrador in which large oil discoveries have been made in recent years, making it a promising site for future offshore oil and gas developments. The site is located approximately 200 kilometers North-East of the currently producing Jeanne D’Arc Basin. This results in some additional challenges, including: higher waves and rougher seas on average, longer transit time from shore to any potential production facilities, and an increased risk of sea ice. Crew transfers from Offshore Supply Vessels (OSVs) to current production platforms offshore Newfoundland and Labrador are typically accomplished with a FROG-6 personnel-transfer capsule lifted by a platform-board crane. In current practice, for fixed platforms, this is only done when there is a Significant Wave Height (Hs) of 4.0 m or less, regardless of the OSV being used. In the winter months, this general-purpose approach does not allow for an acceptably high operational fraction of time in which crew transfers could be completed in the Flemish Pass.

The FROG-6 capsule has designated operational limits based on the relative velocity between the capsule and the vessel deck, which will vary based on ship size, loading condition, and sea-state. Considering this, a series of geometrically similar OSV hull forms are created to represent the range of currently operating vessels. The developed models are between 70.0–90.0 m long, have a maximum breadth between 17.0–22.0 m, and block coefficients ranging from 0.65–0.79. Using ShipMo3D, a potential flow / panel code seakeeping solver, a 20 minute time history of ship motions is determined for all the modelled OSVs, across the range of sea-states realistically expected in the Flemish Pass. Then, a MATLAB script is used to transform these motions into deck velocities. From these results, the operational limits for crew transfer can be re-defined as a function of ship size, loading condition, and sea-state. This results in higher operability percentages than those achieved from using the flat wave height limit alone, with relatively large variations between differently sized and loaded ships. Further work must be done to officially implement new limits, such as: analysis of additional wave period and height combinations, further analysis of the time between limit exceedances, computational fluid dynamics simulations, “smart crane” modelling, and/or full scale sea trials.
On the Array of Wave Energy Converters: The Case of the Coaxial-Duct OWC
Authors: Portillo J. C. C. , Henriques J. C. C. , Gomes R. P. F. , Gato L. M. C. , Falcão A. F. O.
Published: September 2018

This work focuses on the initial performance assessment of an array of coaxial-duct (CD) oscillating-water-columns (owc’s) with potential to be used as multipurpose platform for the creation of value in a diverse range of offshore economic activities. The coaxial-duct owc (CD-owc) is an axisymmetric oscillating-water-column wave energy converter that has been studied for both small-size and large-size applications. This work focuses on buoys of 12 meter diameter distributed in an array of five devices, rigidly attached to each other, to form a cluster of owc’s. The objective of the study is to assess the performance of the array with this configuration and estimate the effect of parameters such as distance between devices, various modes of movements, and other constraints on the overall power output of the array. Results of different cases are compared to the performance of an isolated device to determine the interference effect of other devices. Some results validate previous research conclusions and new findings on the behavior coaxial-duct owc are presented.
Numerical Analysis on the Response of Deck Plates Laterally Impacted by a Rectangular Indenter
Authors: Zhu Ling , Gao Junying , Li Yinggang
Published: September 2018

Ship deck plates are often subjected to localized dynamic loads, such as the loads of landing helicopter or impacts of ice floes. In order to investigate the dynamic response of ship plates subjected to such dynamic loads, a series of numerical simulations are performed on ship plates with different thicknesses. Parametric studies are performed on the impact response of plates, including the thickness of the plates, mass and impact velocity of the rectangular indenter. The maximum permanent deflections of the plates are obtained during the simulation. The relation between maximum force and permanent deflection is obtained and the deformation modes are analyzed. A theoretical procedure is developed to predict the deformation of plates with different initial impact energies, and a good agreement between the theoretical and numerical results is obtained. It has also been observed that the thickness of plates has little effect on the dimensionless maximum permanent deformation and dimensionless maximum impact force.
Development of a Welding Sequence Optimized for the Fatigue Resistance of Tubular Joints With a Novel Representative Welded Sample
Authors: Thibaux Philippe , Van Pottelberg Eric
Published: September 2018

Tubular joints are complex geometries present in many offshore structures. Fatigue testing of tubular joints requires either downsizing of the dimensions of the joints or the use of a simplified geometry, to avoid prohibitive costs. For the development of a welding process optimized for the fatigue performance of tubular joints, one needs to use a representative sample: same material, same thickness, use of similar welding positions, same level of restraint as in a real structure, combined with the supplementary requirement of ease of manufacturing and testing.

A novel geometry was developed to fulfil all these requirements. Then, different welds were produced using robot and manual welding in different positions. The fatigue tests proved to be very reproducible, and indicate a strong influence of the welding position on the fatigue resistance. For that reason, an optimized welding procedure and sequence was developed, in which the welds in the most fatigue sensitive locations are produced first in optimum condition, while the less sensitive parts are produced by subsequent welding in position.
Numerical Simulation of the Complex Impact Behavior of Float-Over Deck Installation Based on an Efficient Two-Body Heaving Impact Model
Authors: Zou Meiyan , Zhu Ling , Chen Mingsheng
Published: September 2018

Float-over deck installation involves multi-body interactions under the wave excitations, such as the nonlinear impacts between the barge and deck via the Deck Support Units (DSUs) and between deck and substructure via the Leg Mating Unit (LMUs). These nonlinear impacts can only be analysed in the time-domain. This paper develops an efficient two-body heaving impact model based on the Cummins equation to study the nonlinear impact behaviour of float-over deck installation. In this model, the convolution term of the Cummins equation is replaced by state-space model such that the efficiency of time-domain modelling can be greatly enhanced. Both the DSUs and LMUs, serving as the shock absorbing devices, are modelled as linear compression-only springs with limited carrying capacity. When the carrying capacity of DSU and LMU is reached, direct contact between deck and barge and between deck and substructure are also modelled by using two harder compression-only springs. The established model is applied to study the nonlinear dynamics of the float-over system during the mating stage that is divided into five stages according to the percentage of deck load transferred to the substructure. Bifurcation diagram is also applied to demonstrate the nonlinear behaviour associated with the deck and barge subjected to LMU and DSU impacts. Hard impacts, namely the direct impacts between the deck and barge and between the deck and substructure, together with high frequency vibrations are found to occur at the start and end of the mating stage. The motion pattern of the deck evolving from periodic motions into chaotic motions is identified. In addition, the period-doubling phenomenon is also observed.
Hydrodynamic Modelling and Performance Evaluation of Cycling Varying Pitch Propeller in Non-Uniform Wake Field Using Open-Water RANS CFD Simulations
Authors: Freiberg Uffe Sjølund , Andersen Torben Ole , Nielsen Jens Ring
Published: September 2018

The cyclic varying pitch propeller is a controllable pitch propeller that is able to change the pitch of the propeller blades individually during one revolution in order to compensate for the non-uniform wake field. By changing the pitch to compensate for the non-uniform wake field, the unsteady phenomena such as cavitation, vibration and noise can be reduced. This gives new possibilities when designing the propeller blades, which can result in a higher propeller efficiency. In order to make the blade design, the actuation mechanism and determing the optimum blade pitch trajectory, it is necessary to determine the hydrodynamic loads acting on the propeller blades due to the non-uniform wake field. An unsteady CFD simulation of the cyclic varying pitch propeller in a non-uniform wake field is computational expensive and is not suitable for determining the optimum pitch trajectory in an iterative manner. Hence, it is desired to have a less computational expensive method to calculate the optimum pitch trajectory. A simple method to characterize a propeller is to determine its open-water characteristics. It is therefore reasonable to try using the propellers open-water characteristics to determine the hydrodynamic loads in order to obtain a less computational expensive method. In this paper, the propellers open-water curves are determined for a range of pitch settings through steady state RANS CFD simulations. To avoid making an erroneous conclusion, the uncertainty of the simulation results are determined. The propellers open-water curves are used to evaluate the thrust and efficiency for the cyclic varying pitch propeller which are compared to the controllable pitch propeller.
Study of Viscous Effects on Wave Drift Forces on a Rectangular Pontoon With a Damping Plate by Using CFD Code OpenFOAM
Authors: Courbois Adrien , Tcheuko Emmanuel , Bouscasse Benjamin , Choi Youngmyung , Kimmoun Olivier , Mariani Riccardo
Published: September 2018

Wave drift loads play a key role in station-keeping analysis of floating offshore structures. However, conventional radiation/diffraction tools have some limitations especially when the structure has sharp edges, requiring more extended validation. In this paper, a series of CFD computations are performed on a 2D simplified shape representing a rectangular-pontoon, with or without a horizontal damping plate. In the present study, the structure is considered to be fixed (radiation effects are not included). For validation, the results of CFD are compared with the results of experiments. The model tests are performed at the wave canal with an equivalent configuration. The drift forces are derived from the reflected and transmitted waves thanks to far field formulation. The incident, reflected and transmitted waves are separated by using a multi “sensors” method. The dissipation of wave energy is also investigated. The analysis is performed on two different model configurations: with and without the presence of a bottom damping plate. The effect of the damping plate on the wave energy dissipation and drift forces are discussed. The results obtained allows for a better understanding and will allow the study on more complex configurations.
PFC-2D Numerical Study of the Influence of Passive Vibration Assisted Rotary Drilling Tool (pVARD) on Drilling Performance Enhancement
Authors: Alwaar Abourawi , Abugharara Abdelsalam N. , Butt Stephen D.
Published: September 2018

The objective of this work is to evaluate the influence of the implementing the downhole Passive Vibration Assisting Rotary Drilling (pVARD) Tool on enhancing drilling performance using a numerical study utilizing a Particle Flow Code (PFC-2D). The work is comprised of a numerical study of a simulation using the PFC-2D on an experimental work described in ARMA 15-492 (Rana et al, 2015). The numerical study was performed to validate the experimental work following the steps, procedure, and conditions performed in the laboratory work.

The numerical study of the laboratory work involves not only the evaluation of drilling rate of penetration (ROP), but it also includes the Depth of Cut (DOC) of the bit cutters and the Mechanical Specific Energy (MSE). This numerical work also includes comparison study of drilling performance under various configurations of the pVARD tool, which represents a controlled downhole vibration against the rigid drilling configuration that represents the conventional rotary drilling. The pVARD configurations involves pVARD low spring compliance, medium spring compliance, and high spring compliance. The drilling output parameters of DOC, MSE, and ROP are then studied and analyzed in all pVARD and non-pVARD configurations.

Likewise of the experimental work, the result of the numerical simulation approves the experimental work and it indicates the positive effect of utilizing the downhole pVARD on improving ROP. The drilling performance enhancement is also supported by the DOC and the MSE result.
Petroleum Exploration Using New Technologies in 3D Seismic Operations in Arctic Environment - North Slope Alaska
Authors: Rodriguez Luis , Uribe Juan , Munoz P. A. , Parrado Roberto , Sanabria Nestor
Published: September 2018

Oil exploration in arctic regions is a very complex activity taking place in a sensitive environment, highlighted by social, wildlife and extreme weather conditions restricting operations to a very limited time window based on the opening of the Tundra season regulations which assesse the quality of the ice and snow coverage over frozen tundra, lakes and seas.

Thanks to new technologies, oil exploration in the arctic environment takes a great steps in 3D seismic acquisition methods passing from cable recording equipment and the dependence of sensor connectivity to a recording center and replacing this system with a very versatile system of wireless receivers units equipped with GPS positioning and time stamp recording and storing the seismic data “in situ”.

This new technology has allowed a high unit count of light receivers to operate in extreme conditions, which in the past was practically impossible given the limitations of the logistical support to carry out this type of operations in remote and difficult access areas. Definitely this technological development has allowed Repsol to explore a larger surface area in a single winter season acquiring high resolution seismic data that allows obtaining high quality images with better geophysical attributes.

Seismic sources have also undergone a notable evolution through the use of high productivity techniques of vibrating trucks moving from a set of multiple vibrators to a single vibrator emission getting up to date simultaneous source acquisitions which allows recording more information without waiting for a second set of vibrators or single vibroseis truck to start shaking to emit energy to the ground. The ability to vibrate at the same time with many sets of single vibrators allows operation on frozen sea either with grounded ice or vibrating on floating ice expanding the exploration boundary to the open sea zones.

The new technology has made it possible for Repsol to improve the operational capability of the crew without increasing the number of people or increasing the logistical support required to operate in remote and difficult access areas. This technological advance has allowed the improvement of the quality of oil exploration using 3D seismic techniques reducing the price per recorded trace or per surface source, increasing the possibility to acquire larger surfaces and better seismic data in a single winter season window. More importantly, these technologies have allowed affordable oil exploration with a high respect for the communities, the wildlife and the environment.