bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Influence of Atmospheric Stability on the Wave Climate in a Warm and Saline Water Body
Authors: Golestani Maziar , Jensen Palle Martin , Kofoed-Hansen Henrik 
Published: October 2015

This paper presents some of the challenges faced during a project aimed at preparing long-term wave climatology in the Persian/Arabian Gulf. Using the hourly CFSR wind fields as forcing, an attempt was made to produce a comprehensive hydrodynamic and sea state conditions data set. By comparing the wave results to various in-situ and satellite measurements, an obvious seasonal difference was observed. Wave conditions were well reproduced during winter while the wave height was generally overestimated and scattered during the summer period.
After comparing the wind fields against measurements it was believed that other sources were playing an important role in wave growth and propagation. Based on available measurements, it was shown that in the summer period, where the air temperature is higher than the sea temperature, wave growth rate is lower than in the winter period. Similar real cases have been reported in some lakes, but the influence of atmospheric stability on wave climate in a relatively large sea like The Gulf has not been documented yet to the authors’ knowledge. This paper focuses on the importance of including atmospheric stability effects into wave modelling. In order to account for the stability effects, the friction velocity and surface roughness were modified in the 3rd generation wind-wave model, MIKE 21 SW, using the Monin-Obukhov similarity theory. Improvements were seen in the quality of modelled wave heights in the summer period. The Gulf is also highly affected by changes in the sea water density. The effects of varying water density on wave climate were also studied in this paper. In order to reproduce the best quality wave climatology in The Gulf, it was concluded that seasonal modelling is required and the effects of atmospheric stability should be included.
Global In-Place System Behavior of Flexible Pipeline on Seabed
Authors: Brankovic Maša , Vervik Stian , Løken Erik , Damsleth Per 
Published: October 2015

A pipeline system consists of the flexible pipe and all associated ancillary components up to the connecting components at battery limits. The global system design deals with aspects related to the overall flexible pipe system — not cross-section or component design. Key system design issues to address are specified in ISO 13628-11:2007 (API 17B) and include general system design requirements, flowline design requirements, and interfaces involving different contractors and suppliers. Unlike unbonded flexible risers that operate in tension, flexible pipe laying on the seabed will be subject to compressive forces and global buckling as for rigid pipelines.
The global flexible pipeline system design will use relevant design codes such as ISO 13628-11:2007 and API 17B / 17J. Yet, the terminology and what such design encompasses can be interpreted differently amongst the community of flexible designers, installers and operators. Failure modes, for example, are not perceived in the same way. While axial compressive force may not be allowed for a riser design, it is a normal flexible pipe response to expansion when pressurized on the seabed. Pull-in and connection forces and moments may be perceived as maximum loads by installers and subsea equipment suppliers but the pressure-induced hydrotest and operational loads may exceed these and overstress the piping leading to a HISC failure.
The system functional requirements for flexible pipelines are similar to rigid lines but when it comes to a flowline laid on the seabed, exposed to pressure and temperature, the methodology for establishing accurate predictable global behaviour is still under development in the industry.
To perform the global in-place design of a flexible flowline, a detailed understanding of the effects of pressure and temperature on the unbonded flexible construction with respect to its bending stiffness and expansion and the limiting criteria stipulated by the manufacturer is needed. The flexible’s behaviour can be simulated using a 3D FE model capturing the effects of seabed surface variations, interaction with soil, and entire load history from installation, to flooding and hydrotest to filling with product at a range of pressures and temperatures including start-up shut-down cycles. Whereas general requirements are stipulated in API 17, specific guidelines applicable to global buckling design are found in DNV-RP-F110 for rigid pipelines. This predictive analysis methodology using risk-based design criteria provides the basis for a robust design that can accommodate large variations in installation tolerances, uneven seabed, varying soils, etc., while providing all concerned with a sound understanding of the flexible behavior and interface loads throughout its design life.
Integrity Assessment of a Free-Fall Lifeboat Launched From a FPSO
Authors: Ji Guomin , Berchiche Nabila , Fouques Sébastien , Sauder Thomas , Reinholdtsen Svein-Arne 
Published: October 2015

The paper addresses the structural integrity assessment of lifeboat launched from floating production, storage and offloading (FPSO) vessels. The study is based on long-term drop lifeboat simulations accounting for more than 50 years of hindcast data of metocean conditions and corresponding FPSO motions. Selection of the load cases and strength analyses with high computational time is a challenge. The load cases analyzed are those corresponding to the 99th percentile of long term distribution of indicators for large slamming loads (CARXZ) or large submergence (Imaxsub). For six selected cases, the time-varying pressure distribution on the lifeboat hull during and after water impact is calculated by CFD simulations using StarCCM+. The finite element model (FEM) of the composite structure of the lifeboat is modelled by ABAQUS. Quasi-static finite element (FE) analyses are performed for the selected load cases. The structural integrity is assessed by the maximum stress and Tsai-Wu failure measure.
In the present study, the load and resistance factors are combined and applied to the response. A sensitivity study is performed to investigate the non-linear load/response effects when the load factor is applied to the load. In addition, dynamic analysis is performed with the time-varying pressure distribution for selected case and the dynamic effect is investigated.
Spatial Variability of Extreme Sea States on the Irish West Coast
Authors: Clancy C. , Belissen V. , Tiron R. , Gallagher S. , Dias F. 
Published: October 2015

Recent studies have revealed a long history of large waves around Ireland, which can be attributed to persistent strong winds in this area. At the same time, due to the consistently high levels of wave energy, the West Coast of Ireland has attracted a lot of interest as a prospective site for deployment of wave energy converters (WECs) farms. The design of such devices, and in fact of any offshore installation, depends crucially on the knowledge of extreme sea states they will experience during their deployment time.
With this in mind, an Extreme Value Analysis incorporating seasonality and accounting for long-term trends was performed, based on a 29 year hindcast for Ireland. The hindcast was performed using the WAVEWATCH III wave model in a 3 nested grid setup, with the largest grid covering the North Atlantic basin and the finest resolution grid (10km) focusing on Ireland. The model was forced with ERA-Interim 10m winds from the European Centre for Medium Range Weather Forecasts. The wave model was validated by comparison to buoy data from the Irish Marine Data Buoy Network.
The analysis was performed on the entire fine resolution grid. This affords a characterisation of the spatial variability in extremes both along the coast and with depth gradients. This is of interest in many marine applications, and in particular WEC design and deployment. Indeed, in the nearshore, wave energy levels can be similar to those found in the offshore. This, in conjunction with the diminished risk of extreme sea states, makes nearshore areas attractive for future ocean energy sites.
Tubarão Martelo Field Development: Lazy S Riser Configuration Using Mid Water Arch (MWA)
Authors: Ribeiro Elton J. B. , Labanca Edson Luiz , Bartz Cesar , Iwane Andre 
Published: October 2015

Mid-Water Arches (MWAs) have been used as alternative to distributed buoyancy systems in flexible riser designs worldwide. Those structures usually involve complex lifting requirements for installation, as the Buoyancy Tank Assemblies (BTAs) are lightweight compared to its volume and footprint area. Handling those odd-sized structures in the deck of a construction vessel and crossing the splash-zone are frequently challenging engineering tasks.
This paper will present a case study of MWA installation performed by GE/WSC as part of the OGX Tubarão Martelo field development, offshore Brazil. The location is prone to swell from South Atlantic and hence a flat sea is a rare event, even when no local wind generated are present. This makes any delicate and weather sensitive operation a critical schedule issue. Still, 8 MWA were installed with minor Waiting on Weather thanks to an extensive analysis envelope and to an engineered installation method aiming to minimize the time the operation was limited by weather condition.
Also, as the scope involved a large number of MWAs, a “mass production” method was developed for the operations, not only covering the offshore installation but also the mobilization and logistic aspects of handling large and heavy items ashore. To allow road transportation by trucks, the BTAs and Gravity Bases (GBs) were shipped to the mobilization port in sub-components for site integration.
Comparison of Numerical Models and Verification Against Experimental Data, Using Pelastar TLP Concept
Authors: Vita Luca , Ramachandran G. K. V. , Krieger Antonia , Kvittem Marit I. , Merino Daniel , Cross-Whiter John , Ackers Benjamin B. 
Published: October 2015

The analysis of a FWT is a complex problem, which requires advanced tools. Several numerical solutions have been used to couple hydrodynamics and aerodynamics and some of the available numerical tools have been compared in code-to-code comparisons. However the code validation for analysis of FWTs is limited by the number of available experimental data.
In the present article, DNV GL and Glosten present a code comparison of four numerical tools against model test results. The design used for the analysis is the Pelastar Tension Leg Platform (TLP) by Glosten. A 1/50 downscaled model of the platform and NREL-5 MW wind turbine was tested in MARIN ocean basin. The results from the model tests are used to verify the results from the numerical codes. The FWT is modelled using four different codes: HAWC2 (by DTU and used by DNV GL), BLADED (by DNV GL and used by DNV GL), SIMA (by Marintek and used by DNV GL) and ORCAFLEX (by Orcina and used by Glosten). Although differences exist among these codes, comparable approaches have been used.
Results from the numerical codes are compared against the experimental data, in terms of:
- Natural periods
- Response in regular waves
- Response in irregular waves
- Response in irregular waves with aerodynamic loads.
In general, the results show a good agreement between the different numerical models and all the codes are capable to reproduce the main dynamics of the system. Some deviations were found and should be solved, in order to use these models for a detailed analysis. However these differences do not seem to be due to limitations of the codes and they might be solvable with a more accurate model of the system.
The Effect of Different Oil Based Drilling Fluids on Mechanical Friction
Authors: Ytrehus Jan David , Taghipour Ali , Golchin Arash , Prakash Braham , Saasen Arild 
Published: October 2015

A very important aspect in highly inclined wellbores is the mechanical friction. For extended reach drilling (ERD) and through tubing extended reach drilling (TTERD) this can be a limiting factor. Friction caused by the contact between the drill string and the well casing or borehole is dependent to the drilling weight and fluid properties. Drilling fluids play an important role on mechanical friction and using oil based drilling fluids with higher lubricity can reduce torque and drag behavior and minimize stick and slip. Reducing mechanical friction will improve drilling efficiency in general, and will in particular enable longer reach for ERD wells.
This paper presents results from experimental laboratory tests where mechanical friction has been investigated. The experiments have been conducted as part of a project in the Tribolab at Luleå University of Technology in cooperation with Det norske Oljeselskap.
Friction behavior has been investigated for different drilling fluids; water based and oil based drilling fluids both with and without solid particles. A pin on disc setup was used for these experiments where a spherical steel pin was sliding on a rotational disc made of granite. Friction force has been measured in constant sliding speed and in presence of particles in wet condition. The test results show that mechanical friction in general is smaller with oil based than water based drilling fluids in the presence of solid particles. In addition, the friction coefficient increases when solid particles were added to the lubricants.
Such experiments in a tribology laboratory are important to identify the effect of drilling fluids on mechanical friction from a basic point of view and isolated from all other wellbore parameters. It is interesting to monitor if the results from this setup can have quantitative relevance also for field situations and such comparison should be done as follow up. Test results and the experimental approach could therefore be of value for any one working with drilling and well construction.
Comparative Review of the Established UHB Assessment Methods for Offshore Pipelines
Authors: Kumar Sajith , Smith Daniel , Jafari Hooman 
Published: October 2015

Out of straightness upheaval buckling (OOS UHB) assessment considers the pipeline design and operational parameters, post-lay survey data and the properties of back-fill and rock in order to determine load and resistance factors that are applied. The factors allow for the natural variation of all parameters and are ultimately used to determine the download requirements along the route of a pipeline that is susceptible to UHB. Two methods are most commonly used in OOS UHB assessments.
The structural reliability analysis (SRA) method is the most established and explicitly considers the variation of parameters in a Monte-Carlo simulation, enabling load and resistance factors to be calculated with a defined reliability level. A more recently developed methodology is documented in DNV-RP-F110 and provides a unified approach to the calculation of safety factors. The approach was calibrated using structural reliability based methods, undertaken with target reliability levels that are compliant with DNV-OS-F101.
This paper presents a review of two key components of OOS UHB assessments. These components are the accuracy of post-lay survey data and the load resistance factor calculation method. These components are reviewed in the context of SRA and DNV-RP-F110 based assessments for a range of pipeline sizes, and ranges of soil and operational parameters. This enables characterisation of the differences between the two methodologies for ranges of design parameters that represent the majority of in-field flowlines that are installed in the United kingdom Continental Shelf (UKCS). SRA and DNV-RP-F110 derived load and resistance factors are compared and the effect of survey data smoothing upon rock-dump requirements is also discussed.
Rheological Properties of Oil Based Drilling Fluids and Base Oils
Authors: Oltedal Velaug Myrseth , Werner Benjamin , Lund Bjørnar , Saasen Arild , Ytrehus Jan David 
Published: October 2015

Drilling fluids for oil wells must meet a number of requirements, including maintaining formation integrity, lubricating the drill string, and transporting cuttings to the surface. In order to satisfy these needs, drilling fluids have become increasingly complex and expensive. To ensure safe and efficient drilling, it is vital for the drilling operator to be able to make a qualified choice of fluid appropriate for each individual well.
API/ISO standards specify a set of tests for characterization of drilling fluids. However, fluids that are tested to have equal properties according to these standards are still observed to perform significantly different when used in the field. The aim of the full project is to provide a thorough comparison of drilling fluids in particular with respect to hole cleaning performance, in light of the issues presented above. As part of this investigation we here present results for two oil based drilling fluids, as well as for the corresponding base oil. The drilling fluids differ in composition by varying fraction of base oil, and thus density and water content.
The fluids have been tested according to the API standard, and further, viscoelastic properties have been examined using an Anton Paar rheometer. The rheological test campaign includes determination of the linear viscoelastic range (LVER), viscosity and yield point, thixotropic time test, and temperature dependence of rheological parameters.
Further, it is demonstrated how the rheological data may be used to interpret data from ongoing full scale flow loop experiments with the same fluids. In a more general context, the rheological test campaign of the drilling fluids is expected to make a crucial contribution for the petroleum industry in explaining observed differences in hole cleaning properties beyond what todays API/ISO industry standard provides.
Numerical Analysis of FPSO Behavior in Ocean Towing
Authors: Zhan Dexin , Spencer Don , Molyneux David 
Published: October 2015

This paper presents numerical analysis of the behavior of a towed FPSO using an in-house computer code Ship Maneuvering Laboratory (SML). The background of the study was an attempt to explain some unexpected observations during a towing situation, where the position of the towed vessel was on the upwind side of the towing vessel and oscillating in yaw. The effects of rudder, wind and current were investigated initially. Then the study focused on the behavior of the towed FPSO with different hydrodynamic coefficients in an environment of steady wind varying from 1.0 to 25 knots with the wind direction on the starboard bow of the tug. The tug was assumed to move in a straight line at a constant speed.
It was found that with the calculated MMG coefficients the FPSO had large oscillations of track and yaw when the wind speed was low (1 knot). When the wind speed was increased, the FPSO moved to the starboard side of the tug (up wind) and kept oscillating and yawing but with less amplitude. This was similar to the FPSO behavior observed in the incident. This phenomenon of oscillating and yawing of the FPSO was not seen when using the measured PMM hydrodynamic coefficients. One possible explanation for the FPSO behavior in the incident was related to the specific values of the FPSO’s hydrodynamic coefficients.
Some possible methods to reduce the FPSO yaw oscillation are also provided. Numerical results showed that by adding drag created by a drogue to the FPSO or using a longer towing bridle can significantly increase the directional stability of the FPSO. A sensitivity study of the FPSO hydrodynamic coefficients is also given and some conclusions are provided.
Development of a FPSO Motion Simulator
Authors: Zhan Dexin , Thanyamanta Worakanok , McDonald Jason , Molyneux David 
Published: October 2015

This paper presents the development of a motion simulator for a moored FPSO, which includes numerical prediction of the FPSO motions in wind, waves and current. It also presents the resulting mooring line tension, 3-dimensional visualization of the FPSO motion, and summary analysis of the resulting motion parameters. The FPSO motion in waves was simulated using an in-house seakeeping code, MOTSIM. A spread mooring line routine, based on catenary theory, was developed and added to MOTSIM to calculate the restoring force of each mooring line. The visualizer (or animator) was developed in-house from open source software, including Ogre, Hydrax and Skyx. It can playback a 3-dimensional view of the simulation (above and below water). The user can view the results in a movie-like format, and change viewing position during the play-back. The user can also run a new simulation from the animator by inputting the required parameters.
The program for analyzing the time dependent responses generated by MOTSIM was developed as a stand-alone program using MATLAB. The analyzer can conduct statistical analysis of time-domain response signals.
A heading control system and a DP control system were also developed in the simulator and can be activated to help control the FPSO motion if required.
A validation of the ship motion prediction and mooring tension was conducted against model experiments using 100-year return period environments with different combinations of wave, wind and current directions.
The simulator was developed as a forecasting tool to help operators predict platform performance based of forecast weather conditions.
Free-Span Flowlines Resistance to In-Service Fatigue Loading
Authors: Iob Francesco , Mecozzi Elisabetta , Di Vito Luigi , Darcis Philippe , Marines-Garcia Israel , Quintanilla-Carmona Hector M. 
Published: October 2015

Offshore petroleum fields frequently pass over areas with uneven seafloor. In such cases the pipeline may have free spans due to depressions crossing and are subjected to complex loading spectra. A major source for dynamic stresses in free span pipelines is vortex induced vibrations (VIV) caused by steady current since wave induced velocities and accelerations will decay with increasing water depth.
The complex loading spectrum differs sensibly from the constant amplitude loading commonly adopted for qualification of the product (line pipe and its girth welds). Centro Sviluppo Materiali and Tenaris for some years are involved in the study of in-service variable amplitude fatigue loading of risers trough numerical calculations and comparison of the actual fatigue loading experienced by free span system with constant amplitude qualification typical loading. Two papers [1, 2] have been already presented in previous OMAE conferences. The present work reports a study dedicated to the free-span flow lines.
The flow line analyzed is composed by OD 273.05 mm × WT 25.4 mm pipe lying on the uneven seabed. In particular the attention is focused on the analysis of VIV and its effect on fatigue life of the line. The Ormen Lange field, located at 120 km northwest of the Mid-Norway, was selected as reference scenario for the study.
One of the most important factors influencing the pipeline response to the VIV is the free-span length. A sensitivity analysis about the influence of different parameters (free span length and fluid velocity) on system response and consequent fatigue damage has been performed.
A case study has been selected among the cases considered in the sensitivity analysis, to produce the loading spectra to be considered in a laboratory fatigue testing campaign on strip specimens.
The fatigue performance of these samples has been compared to analogous samples subjected to constant and variable amplitude loading available from previous works [1, 2] on riser systems (Steel catenary riser and Hybrid riser).