bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thruster-Interaction Effects on a DP Shuttle Tanker - Wake Flow Measurements of the Main Propeller and Bow Tunnel Thrusters
Authors: Cozijn J. L. , Hallmann R. 
Published: September 2014

This paper discusses thruster interaction effects for a DP shuttle tanker, equipped with two main propellers and rudders, as well as two bow tunnel thrusters. Thruster-interaction model tests were carried out in MARIN’s Deepwater Towing Tank. Detailed PIV measurements were taken of the wake flow behind the main propellers and rudders. Furthermore, PIV measurements were taken of the wake flow of one of the two bow tunnel thrusters. The flow velocities were measured in a large number of cross sections at different down-stream positions. The PIV measurements provide a detailed image of the velocities in the thruster wake, showing axial velocities, as well as transverse and vertical velocity components.
The results of the first set of measurements showed in detail the wake flow behind the main propeller of the DP shuttle tanker. The wake flow pattern was determined at rudder angles of 0 deg and 10 deg. Since the research is related to DP performance, bollard pull conditions (zero forward speed) were considered in the model tests.
The results of the second set of measurements showed in detail the wake flow of one of the bow tunnel thrusters. The wake flow pattern was investigated in zero speed conditions, as well as for the vessel at forward speed. The observed flow patterns helped to explain the reduced bow tunnel performance at forward speed.
The results of the present research are used to further improve the understanding of the physics of thruster interaction effects. Furthermore, the results will serve as validation material for CFD calculations that are currently being performed.
A Method for Determining Quasi-Static and Dynamic Riser Inclination Using Collocated Accelerometers and Angular Rate Sensors
Authors: McNeill Scot , Angehr Paul , Kluk Dan , Saruhashi Tomokazu , Sawada Ikuo , Kyo Masanori , Miyazaki Eigo , Yamazaki Yasuyuki 
Published: September 2014

A method is described for determining quasi-static and dynamic riser angles using measured data typically found in a riser fatigue monitoring system, specifically acceleration and angular rate data. Quasi-static riser inclination and orientation of the inclination plane are determined from the low frequency triaxial accelerations, containing measurement of the gravitational body force. Components of the gravitational body force along the accelerometer axes vary slowly with the riser quasi-static response. The slowly varying Euler angles are determined from the components of gravity along the three axes.
Dynamic riser inclination along and transverse to the quasi-static inclination plane are determined by integration of the angular rates, followed by transformation into a coordinate system aligned with the quasi-static inclination plane. The quasi-static and dynamic inclination angles are combined to arrive at the time trace of riser inclination angles.
Following implementation of the method in Matlab®, the procedure was validated and the program verified using laboratory test data. A double-gimbaled platform was constructed, on which were mounted a triaxial accelerometer, biaxial angular rate and biaxial inclinometer (reference sensor). A battery of static and dynamic tests was carried out on the platform. Machinists’ levels and angle gauges were used to set the inclination in the various tests. The angles derived from the acceleration and angular rate data were compared to those of the reference inclinometer. Angle estimates were shown to match the reference angles with negligible error.
The method was then implemented into the real-time Riser Fatigue Monitoring System (RFMS) aboard the Chikyu drillship. The algorithm was run using data from an emergency disconnect event that occurred in November, 2012. Quasi-static riser inclination angles were quite large due to high currents near the sea surface. Dynamic riser inclination angles proved to be significant due to Vortex Induced Vibration of the lower portion of the riser that immediately followed the disconnect event.
It is important to note that the method uses data that is typically already included in real-time riser monitoring systems. Therefore only a software update is required to provide real-time riser angle information. If the method is built into data processing routines for real-time riser monitoring systems, the need for additional instrumentation, such as inclinometers near flex joints, may be circumvented. On the other hand, if inclinometers already exist, the method serves as an independent source of riser angle information at several locations on the riser. The method can also be used to calculate riser and Blow out Preventer (BOP) stack angles from data recorded using stand-alone, battery-powered loggers.
Warm Model Ice and Propeller Interaction, Capturing the Driving Mechanics?
Authors: Hagesteijn Gerco , Brouwer Joris 
Published: September 2014

In the drive to design robust and more efficient propellers, the need to understand propeller-ice interaction is increasing. Traditionally MARIN has built up this kind of propeller design knowledge by developing and testing large systematic propeller series, such as the classic Wageningen B-series and the recent C and D-series. With systematic variations of blade number, area, pitch and profiles it can be investigated how these parameters influence the design and how the most efficient designs for operation in open water and in ice can be reached. This is becoming especially important for the lower ice class propellers, which are rarely sailing in ice covered areas. Apart from this, these designs should be optimized for low noise emission as well, to ensure application in the sensitive Arctic environment. When both milling and crushing loads can be captured using a warm model ice, the testing of such a large systematic propeller series becomes possible without the use of an ice basin.
In the present paper an evaluation is presented, showing the results of a first series of testing that was carried out with a warm model ice. The test set-up used is one that has also been used for the same kind of tests in a real ice basin. The warm model ice was designed to resemble the correct crushing strength at model scale. The warm ice samples are fed into the propeller, while at the same time the load on one of the propeller blades is recorded with a 6C-load transducer. At the same time the impact is recorded with a high speed video camera. To enable a detailed analysis, the force vector is plotted on the high speed recording. The force vector can be derived using a centre of pressure method. In this way an evaluation can be made if the captured phenomena are indeed similar to those that can be expected from real (model-)ice.
Non-Linear Air Gap Analyses of a Semi-Submersible Compared With Linear Analyses and Model Tests
Authors: Kvaleid Jørgen , Oosterlaak Volkert , Kvillum Tor 
Published: September 2014

For semi-submersible units, the magnitude of air gap or local wave impact in the survival condition is a key design driver. Linear analyses are widely used in the industry to predict survival air gap for semi-subs. Large relative motions, leading to large changes in shape of the submerged hull and large changes in water plane area make this approach questionable.
In this paper, the GG5000 [1], a twin pontoon four legged semi-sub is considered. Both linear analyses and model tests had been performed, but the results were diverging. It was decided to investigate further, using non-linear hydrodynamic analyses.
Initially, the model test setup is reproduced in the numerical model. The simulation model is verified for both response power spectra and extreme response distributions. In the non-linear simulations, the wetted surface of the hull is updated for each time step. Both excitation and restoring forces are based on the instantaneous wetted surface. This proves essential for the prediction of large motions. Later, the verified simulation model is run with realistic full scale setup including elastic catenary moorings with coupled cable dynamics, thruster assist, irregular waves and irregular wind.
Highly non-linear effects proven to be vital to accurate air gap prediction are investigated and their representation in the non-linear analyses is validated against model tests.
Development of a Fatigue Life Assessment Tool for Pipelines With Local Wrinkling Through Physical Testing and Numerical Modelling
Authors: Bakhtyar Fahad , Kenny S. 
Published: September 2014

Pipelines are one of the primary modes to transport hydrocarbon products throughout the world. A majority of these pipeline systems are buried, which are susceptible to ground movement that imposes axial forces and bending moments on the pipeline section. As a result of these forces and moments pipeline section may experience localized deformation that result in wrinkling, buckling and other damage mechanisms. This may impair the pipeline mechanical performance with respect to local stress concentration, lower strength and reduced fatigue life. Cyclic operational loads or ground movement events may result in strain reversals within the pipeline section that may lead to fracture through low cycle fatigue process.
In this study, physical testing was conducted to examine the strength and fatigue life performance characteristics of hot rolled steel (44-W). The effects of the test sample bend radius, wall thickness and imposed displacement stroke range on fatigue performance were examined. The data was used to develop and refine continuum finite element modeling procedures that can be used to assess the influence of pipeline damage on fatigue life in a more detailed numerical simulation framework.
A Comparative Study of Hole Cleaning Performance — Water Versus Drag Reducing Fluid
Authors: Rodriguez Corredor Fabio Ernesto , Bizhani Majid , Kuru Ergun 
Published: September 2014

Effective hole cleaning in horizontal and extended reach wells (ERD) often requires use of high circulation rates, which may not be always achievable due to the risk of circulating bottom hole pressure reaching the fracture limit of the rock. Achieving good hole cleaning while keeping the circulating bottom hole pressure within the safe operational window is very often the major engineering challenge. A drag reducing fluid with good hole cleaning ability could be a potential solution in this case.
In order to see if it is possible to use a drag reducing fluid and still achieve a good hole cleaning, an experimental program was designed and conducted. The main objective of this experimental study was to compare the hole cleaning performances of water and a drag reducing fluid.
The hole cleaning experiments were conducted using a 9m long horizontal flow loop with concentric annular geometry (Outer Pipe ID = 95 mm, Inner Pipe OD = 38 mm, ID/OD ratio = 0.4). The drag reducing additive was a commercially available partially hydrolyzed polyacrylamide (PHPA). Water and two drag reducing fluids with 0.07% V/V and 0.1% V/V PHPA concentrations were used. Critical velocities for the initiation of cuttings movement with rolling, saltation/dunes, and suspension modes were determined and compared when using water and drag reducing fluids as a carrier fluid. Critical velocities for the initiation of cuttings movement were found to be lower with water than that of drag reducing fluid in all transport modes.
Warm Pre-Stressing and Leaks in Pipelines
Authors: Cosham Andrew , Hopkins Phil , Jones David G. , Barnett Julian 
Published: September 2014

Line pipe steel is a carbon manganese steel. The toughness of line pipe steel undergoes a transition from high toughness (on the upper shelf) to low toughness (on the lower shelf) as the temperature decreases.
A fluid will cool significantly as it expands through a leak in a pipeline. This has led to the suggestion that localised cooling of the material surrounding the leak might be sufficient to cool the material down to below the ductile to brittle transition temperature and cause a brittle fracture.
Warm pre-stressing occurs when a load is applied to a structure containing a defect and then the temperature of the structure is reduced. Warm pre-stressing causes the defect in the structure to fail at a higher load at the lower temperature than if it had not experienced this prior loading at the previously higher temperature.
A programme of single edge notch bend tests has been conducted on behalf of National Grid Carbon to demonstrate the beneficial effect of warm pre-stressing in a line pipe steel. The material tested was a sample of 914.4 mm outside diameter, 19.1 mm wall thickness, Grade API 5L X60 line pipe. Single edge notch bend specimens were subject to the ‘load-cool-fail’ cycle and the ‘load-unload-cool-fail’ cycle. The effect of different levels of stable ductile crack growth during the pre-load was also investigated.
Warm pre-stressing is shown to have a beneficial effect. The load at failure in the specimens that had been subject to warm pre-stressing was higher than those that had not been subject to warm pre-stressing, and, in most cases, it was higher than the pre-load. The fracture toughness (in terms of the stress intensity factor) of the specimens that had been subject to warm pre-stressing was 1.4 to 1.7 times higher than that of those that had not been subject to warm pre-stressing. The results of the tests were conservatively predicted using the theoretical models. Also, the results are consistent with previous tests on structural steels.
Therefore, localised cooling of the material around a leak in a pipeline is not predicted to result in a failure.
Floating Concrete Barge Assessment and Inspection Plan: N’Kossa Case Study, a Large Pre-Stressed Concrete Floating Production Unit in Operation in Congo
Authors: Collet Pascal , Vaucquelin Nicolas , Bury Arnaud 
Published: September 2014

The paper describes the way a large pre-stressed concrete Floating Production Unit (FPU) located offshore Congo on N’KOSSA field has been inspected and assessed in order to meet both Bureau Veritas Class and Floating Units Integrity Management System (FUIMS) requirements.
This FPU is the largest existing pre-stressed concrete barge. She was built with high performance concrete, installed offshore in 1996 in 170 m water depth. She has now accumulated 18 years of production.
A significant part of the methodology is based on close inspection for the concrete structure, a graphic assessment of the defects and an implementation of monitoring.
This assessment is done a long time after construction and we had to cope with difficulties relative to the structure size, loss of data, barge in operations off-shore. It gives a good feedback of what we should implement during the design and the construction to keep a clear view of the concrete barge integrity.
Additional Wind/Wave Basin Testing of the DeepCwind Semi-Submersible With a Performance-Matched Wind Turbine
Authors: Goupee Andrew J. , Fowler Matthew J. , Kimball Richard W. , Helder Joop , de Ridder Erik-Jan 
Published: September 2014

In 2011 the DeepCwind Consortium, led by the University of Maine (UMaine), performed an extensive series of floating wind turbine model tests at the Maritime Research Institute Netherlands (MARIN) offshore basin. These tests, which were conducted at 1/50th scale, investigated the response of three floating wind turbine concepts subjected to simultaneous wind and wave environments. The wind turbine blades utilized for the tests were geometrically-similar models of those found on the National Renewable Energy Laboratory (NREL) 5 MW reference wind turbine and performed poorly in the Froude-scaled, low-Reynolds number wind environment. As such, the primary aerodynamic load produced by the wind turbine, thrust, was drastically lower than expected for a given Froude-scaled wind speed. In order to obtain appropriate mean thrust forces for conducting the global performance testing of the floating wind turbines, the winds speeds were substantially raised beyond the target Froude-scale values. While this correction yielded the desired mean thrust load, the sensitivities of the thrust force due to changes in the turbine inflow wind speed, whether due to wind gusts or platform motion, were not necessarily representative of the full-scale system.
In hopes of rectifying the wind turbine performance issue for Froude-scale wind/wave basin testing, efforts have been made by UMaine, Maine Maritime Academy and MARIN to design performance-matched wind turbines that produce the correct thrust forces when subjected to Froude-scale wind environments. In this paper, an improved, performance-matched wind turbine is mounted to the DeepCwind semi-submersible platform investigated in 2011 (also studied in the International Energy Association’s OC4 Phase II Project) and retested in MARIN’s offshore basin with two major objectives: 1) To demonstrate that the corrective wind speed adjustments made in the earlier DeepCwind tests produced realistic global performance behaviors and 2) To illustrate the increased capability for simulating full-scale floating wind turbine responses that a performance-matched turbine has over the earlier, geometrically-similar design tested. As an example of this last point, this paper presents select results for coupled wind/wave tests with active blade pitch control made possible with the use of a performance-matched wind turbine. The results of this paper show that the earlier DeepCwind tests produced meaningful data; however, this paper also illustrates the immense potential of using a performance-matched wind turbine in wind/wave basin model tests for floating wind turbines.
Variables Affecting Fracture Toughness of Welds in T-K-Y Connections
Authors: Panday Radhika , Zhang Shenjia , Ogborn Jon , Narayanan Badri K. 
Published: September 2014

Fracture toughness of tubular welded joints is one of the critical factors affecting the structural integrity and reliability of offshore structures, such as platforms and subsea pipelines. The factors affecting the design fracture toughness of these structures are related to, both, the welding process as well as the chemical composition of the weld metal.
The welding process in this application typically comprises of depositing weld metal in the tubular joints of varying thicknesses through series of weld passes. The number of weld passes required for welding these joints subjects the weld metal to repetitive cycles of heating and cooling. The effect of the thermal cycling introduces significant heterogeneity in the microstructure. This is further exacerbated by the presence of micro-alloying elements such as Niobium (Nb) and Vanadium (V) that form complex carbides, nitrides and carbo-nitrides during post weld heat treatment (PWHT).
The focus of this work is to evaluate the effect of micro-alloying elements on the ductile to brittle transition temperature and the mode of fracture at temperatures relevant to offshore applications. A threshold Nb and V level has been determined for achieving acceptable weld metal toughness. The improvement in the fracture toughness using this approach has been quantified by Charpy V-Notch (CVN) and Crack Tip Opening Displacement (CTOD) measurements. The Ductile to Brittle Transition Temperature (DBTT) has been shown to be shifted to lower temperatures by 25 °C after post weld heat treatment in the welds where the total amount of Nb and V are controlled to less than 40 ppm.
A wet precipitate extraction technique was used to extract precipitates from the welds to establish the presence of fine Nb rich precipitates in the welds with the higher DBTT. The weld deposited with controlled levels of Nb and V was further tested in different joint configurations and base plate thickness. The fracture toughness was evaluated by CTOD testing of the weld in two different thicknesses (50 mm and 70 mm). Increased specimen thickness resulted in lower CTOD values.
Cement Sheath Integrity Implications of Scaled-Down Wellbore Casing-Cement-Formation Sections
Authors: De Andrade Jesus , Sangesland Sigbjørn , Vrålstad Torbjørn , Golan Michael 
Published: September 2014

Many offshore petroleum wells have serious cement sheath integrity issues that imply costly repairs, limitations with respect to short- and long-term use of planned or converted production and injection wells, and safety issues. The annular cement sheath is exposed to a wide variation of thermal and pressure loads that potentiality may result in zonal isolation failure throughout its lifecycle.
While several experimental and numerical work manage to map highly loaded scenarios that leads to radial cracks and micro-annulus generation, little effort has been taken to investigate and quantify the impact of moderate pressure and thermal loads on cement sheath stresses. This paper presents a 2D finite element assessment of impacts of numerous material properties, geometric parameters, pressure and thermal loading variables contributing to cement sheath stresses. A centralized wellbore section of casing-cement-formation is considered, representing a production casing string. This work is conducted as a preliminary effort in order to develop a down-scaled laboratory set-up, that represents realistically the impact of thermal and pressure loads on cement sheath stresses.
This paper introduces a discussion about the capabilities of a down-scaled well section to characterize the stress distribution around the annular cement sheath of a conventional 9 5/8″ production casing. Results indicate that a down-scaled configuration exposed to comparable internal pressure and temperature profile resembles the stress distribution associated with completion and production operations of wells. It is shown that a proper characterization of the cement stress regimes requires the combined effect of pressure and thermal variations.
Sensitivity studies conducted on cement sheath stresses, for both wellbore and down-scaled configurations, have assessed the relative influence of mechanical and thermal properties as drivers of cement stresses. For well operations with substantial wellbore temperature variations such as production and frac job, particularly uncertain parameters such as cement-formation-Young’s modulus and thermal expansion coefficient of cement have shown significant impact on annular cement sheath stresses. In terms of combined pressure and thermal loading, cement stresses have proved to be more sensitive to temperature differential than pressure differential variations.
Numerical Simulation of Vortex-Induced Motion With Free Surface by Lattice Boltzmann Method
Authors: Miyamura Akitaka , Hirabayashi Shinichiro , Suzuki Hideyuki 
Published: September 2014

In this study, numerical simulation of the fluid flow by using lattice Boltzmann method is carried out and the vortex-induced motion (VIM) of a cylindrical floating structure is calculated. The way of calculate the fluid flow, fluid force and floating body’s movement is introduced.
The fluid flow with free surface is also calculated. The height change of water surface exerts the effect to the evaluation of hydrostatic pressure and wave resistance. In this study, the method to express the movement of free surface is introduced.