bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surface Temperature Fluctuations in Ice Indentation Tests
Authors: Turner Joshua D. , O’Rourke Brian J. , Jordaan Ian J. , Taylor Rocky S. 
Published: October 2015

Ice-structure interactions produce numerous, short-lived high pressure zones which transfer the majority of the load to the structure. Ice indentation tests have been used to observe the fluctuations in surface temperature at these zones. Previous investigations have shown that temperature fluctuates inversely to the applied load during cyclic loading. These fluctuations are believed to be due to rapid melting and refreezing cycles in the high pressure zones.
A recent series of small-scale indentation tests investigated surface temperature fluctuations for indentor speeds at three orders of magnitude (0.21 mm/s to 21 mm/s). Freshwater granular ice specimens were grown in cylindrical steel moulds using seed ice and distilled water. A 70 mm diameter indentor with a radius of curvature of 89.6 mm was indented into the ice to depths between 10 and 15 mm. Seven thermocouples were installed in the indentor and made flush with its surface. These were used to measure the surface temperature of the ice during indentation. All tests took place at −10 degrees.
Notable changes in temperature response were observed with changing speed. A steady increase in temperature was observed during low speed tests. Medium speeds lead to fluctuations in temperature due to the presence of spalling and cyclic loading that is consistent with the results of others. Some evidence of the inverse relationship between load and temperature can be observed in the highest speed tests, but the thermocouples sampling frequency was too low to accurately respond to high frequency loading and could not provide clear results.
Tensioned Step Riser Configuration for Ultra-Deep Application
Authors: Tian Yuan , Hou Yucheng , Pires Fabio , Tan Zhimin 
Published: October 2015

This paper presents and compares the results of a research study for an ultra-deep water field development. A total of three riser configurations were modeled with the commonly used commercial software, and both extreme and fatigue analysis were performed. The advantage of tensioned step riser configuration, a patented and innovative riser configuration specially designed for ultra-deep water application, is demonstrated over other traditional configurations such as free-hanging configuration and double-hump lazy wave configuration.
The analysis results indicated that the proposed tensioned step riser configuration has largely favorable features in extreme and fatigue performance for deep water application. The tensioned step riser configuration should be treated as a strong candidate for ultra-deep water flexible developments under substantially harsh environmental loading with worse vessel responses.
Residual Stress Measurement, Finite Element Mapping and Flaw Simulation for a Girth Welded Pipe
Authors: Ficquet Xavier , Serasli Karim , Kingston Ed J. 
Published: October 2015

Optimising the structural integrity of an oil and gas pipeline is hugely important for its productivity and hence profitability. The structural integrity of a pipeline is influenced by factors such as: stress (i.e. applied and residual), material properties, environment, and the size and orientation of contained flaws. For example, whilst in operation, the integrity of a pipeline can be extended by reducing its applied stresses e.g. the flow and pressure of the oil and gas running within. Prior to operation however the integrity of the pipeline can easily be extended by reducing the residual stresses generated during installation or even “negatively pre-loading” the pipeline using residual stresses to help cancel out some of the applied stresses. Therefore understanding the distribution of residual stresses within a pipeline can be of great benefit to Oil and Gas engineers.
In this paper, complementary residual stress measurement techniques are used to obtain near surface and through-thickness residual stress distributions in a fully circumferential butt welded pipe. The deep hole drilling (DHD) method was used to obtain the axial and hoop residual stresses along radial lines through the pipe wall. Near surface measurements on the outer surface of the pipe were obtained using the incremental centre-hole drilling (ICHD) method.
The measurements were made only at limited points in and adjacent to the circumferential weld. In order to estimate the complete residual stress field present in the pipe, a mapping procedure utilising a finite element (FE) method was implemented. This entailed introducing the measured residual stresses into a FE model of the pipe as an initial condition and allowing redistribution. Naturally, the stresses at the measurement locations should remain at their initial values. Consequently, the method was developed to allow redistribution while retaining the measured values. The paper provides these estimates of the full residual stress state present in the pipe based on this mapping procedure. The FE model was then used to simulate the influence of various sizes of flaw on the mapped residual stresses field. An assessment of the acceptability of areas of loss of the wall thickness in internally pressurised pressure vessels was then performed.
Hydrodynamics of Podded Propulsors With Highly Loaded Propellers and in Extreme Azimuthing Conditions
Authors: Islam Mohammed , Jahra Fatima , Ryan Ron , Hedd Lee 
Published: October 2015

State of the art CFD capabilities has enabled the accurate prediction of forces and moments on the propeller as well as on the pod-strut body due to small to moderate azimuthing angles. The capability of CFD to predict the hydrodynamics at extreme azimuthing angles is yet to be demonstrated. The aim of this research is to develop a simulation capability to capture most of the dynamics of podded propulsion systems in regular to extreme operating conditions. The numerical methodologies to evaluate the hydrodynamic characteristics of podded propulsors in puller configurations in extremely oblique inflow and highly loaded condition in open water and the associated results are presented in this paper.
A numerical study is carried out to predict the hydrodynamic forces of a podded propulsor unit in various extreme static azimuthing conditions. An unsteady Reynolds-Averaged Navier Stokes (RANS) solver is used to predict the propulsive performance of the podded propulsor system in puller configuration using both steady and unsteady state solutions. To obtain insight into the reliability and accuracy of the results, grid dependency studies are conducted for a podded propulsor in straight-ahead condition. RANS solver simulation technique is first validated against measurements of a puller podded propulsor in straight ahead condition for multiple loading scenarios. The propeller thrust and torque as well as the forces and moments of the pod unit in the three coordinate directions in straight-ahead condition and at static azimuthing angles in the range of −180° to 180° at advance coefficient of 0.20 are then compared with that of the measurements. Additionally, the velocity and pressure distribution on and around the pod-strut-propeller bodies are presented as derived from the RANS predictions. Analysis demonstrates that the RANS solver can predict the performance coefficients of the podded propulsor in extreme azimuthing and in the highly loaded conditions within the same level of accuracy of the same order of magnitude of the experimental results.
Validation of Crack Growth for an Finite Element Based ECA Procedure for Reel-Laid Pipelines With Under-Matching Girth Welds
Authors: Sriskandarajah T. , Zhou Daowu , Cao Lingjun 
Published: October 2015

There is a concern on the fracture integrity of the partially over-matching or under-matching weld during reel-lay installation where there is large plastic strain in the pipe. Conventional ECA procedures such as BS7910 and DNV-OS-F101 are applicable for fully over-matching welds only, due to limitations in the reference stress solution (or limit load solutions).
The ECA procedure based on 3D finite element (FE) analysis was developed for partially over-matching welds or under-matching. The methodology has been successfully applied to several projects of industry-wide significance, with partially over-matching welds in offshore pipelines. This paper provides a case study validating the crack growth from FE based ECA methodology against the large scale bending trial test where the pipe containing the notched defect was pre-strained under a series of straining cycles. A comparison of the crack growth between 3D FEA and the large scale bending test was presented.
Prediction of Extreme Tensions in Mooring Lines of a Floating Offshore Wind Turbine in a 100-Year Storm
Authors: Hsu Wei-ting , Thiagarajan Krish P. , MacNicoll Michael , Akers Richard 
Published: October 2015

Floating offshore wind turbines (FOWTs) contribute to an emerging green energy technology, by exploiting higher and consistent wind speeds above the ocean. There are several challenges facing the design of mooring system of FOWTs, including installation costs, stability of light-weight minimalistic platforms, and shallow depths (50–300m). The extreme tension in mooring lines of a light displacement platform in shallow-water is dominated by snap loads. This is because light pre-tension requirements in the line may be insufficient to prevent the mooring lines from being exposed to wave motion induced slack and shock events.
In this paper, we present a comparative analysis of a semi-submersible based FOWT exposed to a 100-year storm condition, based on model test data and numerical simulations of well-known industry standard software. The data was obtained from a 1/50th-scale FOWT with the wind turbine modeled after the NREL 5MW wind turbine. The software, OrcaFlex, was used for numerical simulations of the mooring system. NREL’s FAST software was coupled to OrcaFlex to obtain aerodynamic loads along with hydrodynamic load for FOWT analyses. The numerical simulation of the moored FOWT in a 3-hour storm was executed in both the frequency-domain and the time-domain to determine the dynamic behavior of the platform and mooring system, respectively. Snap–type impact events were observed in both test data and numerical simulation. Tension maxima were fitted into extreme value distributions and comparisons are made between simulated and measured data. It is seen that snap events follow a different exceedance probability distribution compared to the cycle-to-cycle tension maxima.
Hydrodynamic Modeling of Large-Diameter Bottom-Fixed Offshore Wind Turbines
Authors: Bachynski Erin E. , Ormberg Harald 
Published: October 2015

For shallow and intermediate water depths, large monopile foundations are considered to be promising with respect to the levelized cost of energy (LCOE) of offshore wind turbines. In order to reduce the LCOE by structural optimization and de-risk the resulting designs, the hydrodynamic loads must be computed efficiently and accurately. Three efficient methods for computing hydrodynamic loads are considered here: Morison’s equation with 1) undisturbed linear wave kinematics or 2) undisturbed second order Stokes wave kinematics, or 3) the MacCamy-Fuchs model, which is able to account for diffraction in short waves. Two reference turbines are considered in a simplified range of environmental conditions.
For fatigue limit state calculations, accounting for diffraction effects was found to generally increase the estimated lifetime of the structure, particularly the tower. The importance of diffraction depends on the environmental conditions and the structure. For the case study of the NREL 5 MW design, the effect could be up to 10 % for the tower base and 2 % for the monopile under the mudline.
The inclusion of second order wave kinematics did not have a large effect on the fatigue calculations, but had a significant impact on the structural loads in ultimate limit state conditions. For the NREL 5 MW design, a 30 % increase in the maximum bending moment under the mudline could be attributed to the second order wave kinematics; a 7 % increase was seen for the DTU 10 MW design.
Influence of Porosity on the Integrity Properties of Butt Welded Super Duplex Stainless Steel Umbilical Tube
Authors: An Xiaoxue , Dobson Alan , Chan Chun Yip 
Published: October 2015

Super Duplex Stainless Steel (SDSS) tube is the main component in steel tube umbilicals for the transportation of hydraulic fluids and chemicals, or gas injection into the subsea well. The umbilical tube is made from seamless tube joined together by girth weld. Therefore, porosity is one of the main weld defects that could be discovered within the welds, and these defects can have significant impact on the execution of the whole project, in term of both schedule and cost.
This paper reviews the design codes and standards relating to the porosity acceptance criteria, and discusses the recent investigation on the influences of porosity (number, size and location) to the stress distribution within the weld. The study was performed using both FEA and practical fatigue test. The results demonstrated that the distance of the pores to the weld surface is a critical parameter to the increase and localisation of stress as the pore starts to interact with the weld root or cap. In addition, significant pore stress interaction has been observed when a bending moment is introduced to the weld. The study has demonstrated that the current porosity acceptance criteria applied to umbilical manufacture in the subsea industry are typically conservative and can be modified.
Spherical Indentation Tests on Confined Ice Specimens at Small Scales
Authors: O’Rourke Brian J. , Jordaan Ian J. , Taylor Rocky S. , Gürtner Arne 
Published: October 2015

A recent series of small-scale ice indentation tests was conducted as a continuation of previous series, to cover additional strain rates and indentor sizes, and to test the effect of scaling. Tests using indentors 10, 20, 40 and 70 mm in diameter attached to a very stiff structure were carried out at indentation rates over three orders of magnitude, while scaling indentation rate with indentor diameter. Slow rates resulted in creep-like response and deep and wide damage zones. As indentation rate was increased, sawtooth loading and random failure activity were observed, together with a thin layer of microstructurally modified ice beneath the indentor.
This latest test series also included indentation tests with a flexible beam apparatus, with the aim of generating locked-in vibrations. It was determined from previous tests that indenting at much faster rates was necessary to produce lock-in with such an apparatus. For this series, two new beam apparatus of differing stiffness and variable natural frequency were fabricated; the beams were designed in a manner that enabled control and testing of the outcome of varying these factors independently. Tests were conducted with either one or two indentors attached. The typical sawtooth behaviour occurred at lower indentation rates, progressing at higher rates into lock-in activity, which occurred over a range of speeds for both beams. The frequency of lock-in vibrations was found to be lower than the structure’s natural frequency, and to increase with indentation speed over the lock-in range. The ice load on the indentor during lock-in activity appears more ‘cusp’ shaped, rather than the assumed sawtooth.
Hydrodynamic Performance of a FPSO in Highly Oblique Flow Conditions
Authors: Islam Mohammed , Jahra Fatima , Ryan Ron , Molyneux David , Hedd Lee 
Published: October 2015

The capability of the viscous-flow solver Star-CCM+ to simulate the flow around a ship in steady oblique motion has been studied. To obtain insight into the reliability and accuracy of the results, grid dependency studies were conducted. Local flow quantities as well as integral variables were compared to measurement values. A FPSO hull form was considered for the simulations as well as experimental assessment of the resistance and flow field at multiple oblique flow conditions. The measurements and simulations have been completed at one draft, one Froude numbers and in 7 inflow conditions (0° to 180° with 30° increments).
The measurements and predictions were made for the resistance in the inflow direction, side force and yawing moment. Additionally, the pressure and velocity distributions around the hull at multiple cross-sections are presented derived from the RANS predictions. Qualitatively, promising results are obtained. For practical purposes however, the accuracy of the results may require further improvement. For the current calculations, the predicted yaw moment is close to the measurements but the side force is under-predicted. Reasons for these discrepancies might be the neglect of trim and sinkage for the FPSO and of the insufficient grid resolution at the bow and stern. This should be studied in future research.
New Methodology for Flexible Riser End-Fittings Fatigue Assessment Based on Remote S-N Curves
Authors: Borges Marcelo Favaro , Vardaro Eduardo , Campello George , Kwietniewski Carlos Eduardo Fortis 
Published: October 2015

Production of oil and gas in the Brazilian pre-salt will face several technical challenges. One of them that is a major concern is the fatigue life of top risers end-fittings. The new ultra-deep water fields will require a complete new fatigue assessment methodology with higher accuracy. Besides that, the historical data of failure for this sort of equipment shows that the current methodology is not quite optimized for floating units operating in deep water fields. With this, even worst results are expected in ultra-deep water fields.
During its assembly inside the end-fitting, the tensile armor wires need to be folded, unfolded and set in position using epoxy resin. This assembly process involves localized plastic deformation and as consequence of this produces a complex residual stress field and also introduces an elastic stress to maintain the wires in position. Both stresses are not actually taken into account in the current fatigue assessment methodology.
Therefore, the aim of this work is to develop and evaluate a new fatigue assessment methodology for top risers end-fittings based on remote S-N curves. The proposed methodology takes into account both residual and assembly elastic stresses. The effect of stress concentration on the tensile armor wire at the region with localized plastic deformation is also evaluated. Basically, the objectives of this investigation will be achieved through the construction of remote S-N curves using a test box that contains the deformed wire embedded in resin representing a single wire physical 2D model of an end-fitting, the so called mid-scale testing. For this investigation, a six inches API end-fitting was selected because it is widely used and most available in the market.
The results produced here indicated that the localized plastic deformation imposed during the folding and unfolding process has a very important detrimental effect on the flexible risers end-fittings tensile armor wires fatigue life, which makes mandatory a revision of the current four-point bending fatigue assessment methodology.
Post-Installed Fiber Optic Pressure Sensors on Subsea Production Risers for Severe Slugging Control
Authors: Eaton Ammon N. , Safdarnejad Seyed Mostafa , Hedengren John D. , Moffat Kristie , Hubbell Casey B. , Brower David V. , Brower Alexis D. 
Published: October 2015

Fiber optic sensors have gained increasing use in monitoring offshore structures. The sensors have successfully monitored flowlines, umbilicals, wells, Tension Leg Platform (TLP) tendons, production and drilling risers, and mooring lines. Fiber optic sensors are capable of monitoring strain, temperature, pressure, and vibration. While the success of fiber optic monitoring has been clearly demonstrated, the sensors are now under consideration for automation applications. This paper details the plausibility of using pressure measurements from post-installed fiber Bragg grating (FBG) sensors with Model Predictive Control (MPC) to suppress severe slugging in subsea risers.
Prior control schemes demonstrate that slugging is mitigated using a topside choke valve. The most effective methods use a pressure measurement immediately upstream of the touchdown zone of the riser; however, the majority of production risers do not have pressure sensing at that location. With advances in subsea clamp design and bonding it is now possible to install a non-penetrating FBG sensor to monitor pressure near the touchdown zone without shutting down production. Stabilizing the two phase flow both reduces vibration-induced fatigue and has the potential to allow increased throughput with relaxed topside processing constraints.
MPC predicts and adjusts for disturbances to avoid pressure and flow instability. The performance of the controller is influenced by sensor location, choke valve response time, and riser geometry. This study demonstrates that severe riser slugging is effectively controlled with MPC and a post-installed, non-penetrating FBG sensor.
Large Scale Experimental Storm Impact on Nourished Beach Using Cobble-Gravel-Sand Mix
Authors: Frandsen Jannette B. , Xhardé Régis , Bérubé Francis , Tremblay Olivier Gauvin 
Published: October 2015

We have investigated beach stability against storm waves. The studies are done in relation to eroded beaches. We are testing a cobble-sand-gravel mixture as a means of using a soft method for coastal protection on nourished beaches. A physical model of an existing beach was built at scale 1:3. The cobble/sand grain size is in 1:3 scale while the gravel is 1:1.5 scale. The large scale experimental flume tests have been set-up in the new outdoor 120 m long flume in Québec city, Canada. The tests were conducted over two test seasons (2013–14). While we in the first test season studied impact on the beach due to incoming regular plunging breakers, the last season contained tests with incoming irregular plunging breakers on the beach with/without tidal variation.
Herein, we primarily report on the wave impact due to irregular plunging breakers on constant and tidal varying water depths. The wave-tide interactions were conducted with a tidal range of 1 m in relation to beaches with steep beach slopes (1:10, 1:5, 1:1). The model inlet significant wave height was 1.1–1.5 m corresponding to equivalent prototype waves in the range of max. wave heights of 6–8.5 m with dominant periods of 12 s in water depth of about 15 m and tidal range of 3 m.
In general, the Equilibrium Beach Profile (EBP) was reached after exposure to about 10,000 plunging breakers or the equivalent of five storms assuming each lasting 3 hours. A cobble berm was formed rapidly on the top of the beach, protecting the backshore against wave action and flooding while finer sediment was transported “offshore”. Beach width reduction was observed when the initial slope of the beach fill material exceeded the equilibrium beach slope. Sediment grain size sorting along the beach profile is discussed and compared to existing beach models, and EBP was compared to several EBP equations.
From a coastal management perspective, in terms of durability, the mixed cobble-sand-gravel material is showing promise as a material to use for coastal protection. It is highly absorbent and the beach tends to maintain its shape over long time when exposed to several storms. However, storm surges in the combination with high tides can results in excessive run-up and potential flood risks. The stabilized beach typically had slopes of 1:7–1:9 independent of the initial slope. We found that irregular seas result in a less pronounced trough in the beach profile in the swash zone than incoming regular plunging breakers. The tidal interaction was further advantageous, naturally shifting the material back and forth. However, other materials and other sensitivity studies are necessary in order to provide firm conclusions about the usage of the cobble-gravel-sand mixture for coastal protection.