bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Analysis of Contact Stresses Between Mooring Chain Links and Potential Consequences for Fatigue Damage
Authors: Bastid Philippe , Smith Simon D. 
Published: November 2013

Design codes for offshore mooring systems recommend proof loading chain links to around 70% of the specified breaking load of the chain (API RP 2FP1, Lloyd’s Register). This is primarily to check that the chain will safely resist the service loads and will not excessively elongate. It is assumed that the proof load also generates compressive residual stresses at the interlink contact region and also at the point of the intrados (KT point) where a high stress concentration occurs during tensile loading. Tests have shown that proof loading improves the fatigue performance of chain under cyclic axial loads.
Elastic-plastic finite element analyses of the proof loading have been performed. These analyses have shown that the proof loading also generates very high tensile residual stresses in the region surrounding the interlink contact zone. This region also experiences significant in-service cyclic stresses under cyclic tension or out-of-plane bending. The combination of the cyclic stresses and high tensile residual stress is of concern and it is proposed that the periphery of the interlink contact zone should be carefully reviewed. It is understood that chain link fatigue at present is only based on the risk of fatigue damage at the KT point.
This paper presents and discusses results of finite element stress analyses of studless chains of different sizes and grades, and show the relative fatigue sensitivity of the KT and contact regions. The chain grade, dimensions and loading regime are shown to be important.
Material Testing for the Prediction of the Effect of Deformation and Aging Thermal Treatments on Collapse Resistance of UOE Pipes
Authors: Serebrinsky Santiago , Mantovano Luciano , Arroyo Fábio , Valdez Martín , Ernst Hugo , Silva Ronaldo 
Published: November 2013

Oil & Gas offshore exploration and production increase continuously in deep waters. This trend requires pipes with increasing collapse pressure (pc), which is the primary design variable. The prediction of pc, based on an appropriate set of input variables, allows for the appropriate design of deep and ultra-deep water projects.
Elastic and plastic material behavior is one of the main factors affecting pc. International application codes (e.g., DNV OS-F101) incorporate the yield strength into their formulas for pc. In the present work, an assessment of the requirements on material characterization tests for a reliable prediction of pc has been performed. The most appropriate testing direction is the transverse compression. Moreover, since for large diameter pipes the plastic strain levels attained at collapse are often below 0.2%, the sample should allow for an accurate determination of compression behavior in this very low deformation range. This is particularly relevant for cold-formed pipes, as with the UOE process.
Based on these guidelines, a testing procedure has been designed. This analysis has been applied to the prediction of the effect of thermal cycles on pc. Calculated values show a very good agreement with experimental pc values determined for a series of UOE processed pipes that had been thermally treated and collapsed.
Wave Drift Forces and Responses in Current
Authors: Stansberg Carl Trygve , Hoff Jan Roger , Hermundstad Elin Marita , Baarholm Rolf 
Published: November 2013

The influence from a current on wave drift forces and resulting slowly varying vessel responses can be quite significant. In this paper the effect is reviewed and further investigated. Several works have been published on this complex topic during the last 20–25 years, while it is only to a little extent taken consistently into account in standard industry tools. Simplified methods are often used, if any, and /or empirical correction from model test data. Thus there is a need to improve standard tools in this respect.
The effects on slowly varying vessel motions and resulting extreme mooring line loads are demonstrated through time series sequences from selected, previous model tests with FPSO’s and semisubmersibles in steep irregular waves. Wave-current interaction effects that can be larger than the effects from current and wind alone are identified. It is also confirmed from these examples that extreme mooring forces usually occur due to extreme slow-drift motions.
An overview description is given of a new, general numerical potential theory code for industry use, MULDIF-2, where wave-current-structure interaction is consistently included as a basic element in the formulation. Main items in the approach are addressed and referred to previous works in the literature. Results from an initial comparison against previous results on drift forces on a vertical column are given, and a good agreement is found. Further verification and validation work is in progress.
Prediction of VIV for Risers With Effective Strakes
Authors: Campbell Brad , Slocum Scott 
Published: November 2013

Accurate prediction of straked riser response can be important for determining the minimum strake coverage needed to ensure adequate riser fatigue life in demanding high-speed current environments. Previously published results from ExxonMobil’s 2003 vortex-induced vibration (VIV) model tests on a long, flexible, straked cylinder showed that strakes can greatly reduce, but may not entirely eliminate flow-induced vibration. The data also showed that the low-amplitude vibrations that persist when the cylinders are straked are different in character from VIV on bare cylinders, suggesting that the strakes are effective in disrupting the alternating vortex shedding mechanism that excites bare-cylinder VIV and that other flow mechanisms may drive the straked-cylinder vibration. This further implies that classic VIV models that have been developed to predict bare-pipe response due to alternating vortex shedding may not be accurate for straked cylinders even if the excitation model (“lift curve”) is adjusted to represent lower excitation levels on strakes.
Classic VIV prediction methods for bare risers rely on special-purpose theoretical models to account for the strongly nonlinear interactions between bare cylinder motion and hydrodynamic excitation. However, for the low amplitudes of vibration observed in tests with straked cylinders, the influence of the cylinder motion on the flow may be less important. In an effort to more accurately predict the performance of strakes, ExxonMobil has recently explored a new approach for predicting flow-induced vibrations for straked risers that neglects any influence of riser motion on excitation, and instead assumes that hydrodynamic excitation can be approximated to useful accuracy by excitation measured on a fixed straked cylinder. New experiments show that this excitation is stochastic, with broad band-width, and that it conforms to relatively simple scaling laws.
The measured stochastic excitation data has been used with a conventional linear random vibration model to predict the response data acquired from the 2003 model tests on the long, flexible, straked cylinder. Comparison shows a dramatic improvement in prediction scatter compared to predictions using a classic bare-pipe VIV formulation with a “lift curve” model of the strake hydrodynamic excitation.
A Possible Failure Mode for Leeward Mooring Lines on a Floating Storage Unit
Authors: Aksnes Vegard , Nybø Terje , Lie Halvor 
Published: November 2013

The floating storage unit Navion Saga at the Volve field in the North Sea suffered from two mooring line breaks in steel wire ropes in 2011. Investigations of the broken ropes indicated that a possible failure mechanism could be high stresses near the wire socket induced by large bending moments in leeward mooring lines. The scope of the current study has been to make a numerical model capable of capturing such behaviour of the steel wire rope and to check if the minimum bending radius could be as low as the rope’s specified minimum bending radius.
The numerical model has revealed a possible failure mechanism. The connecting link plate between the upper chain segment and the upper wire segment lies initially on the seabed. When lifted off the seabed, the link plate and the wire socket will fall to the seabed at a higher speed than the upper wire segment. A transverse wave in mooring line plane propagating towards fair-lead is generated when the wire socket hits the seabed. The wave leads to large curvature in the wire near the socket. Sensitivity studies of the governing parameters have been performed to assess the uncertainties of the numerical model. A modified system is presented and it is shown that the phenomenon which is likely to have caused failure in the original system will not occur for the modified one.
Increasing Water Depth Window for Moored Subsea Structures and Operations With Low Weight Hybrid Ropes
Authors: Amils Xavier , Durmus Beste , Smeets Paul , Boesten Jorn , Davies Peter 
Published: November 2013

This paper introduces new hybrid wire rope concepts by combining steel wire and UHMWPE fibers. These novel High Modulus Hybrid Ropes (HMHR) result in enhanced strength and significant reduction of linear weight compared to steel wire rope (SWR) of equivalent constructions. Compared to fiber ropes (FR) this new family of ropes shows increased protection against crushing, fretting and wear.
In-house and independent laboratory tests showed increased breaking load / weight advantages compared to SWR, while also revealing improved bending fatigue resistance. Additionally, test results show similar axial stiffness and torque performance to SWR, which can be modeled by using analytical algorithms. Furthermore creep rate of these ropes is comparable to that of SWR.
Finally, the authors discuss the expected performance of these ropes working in deep waters and under high load conditions in offshore and subsea systems. Additional work required to validate and introduce these ropes in the industry is addressed as well.
Analysis of Ringing Response of a Gravity Based Structure in Extreme Sea States
Authors: Kim Jang , Tan Jaime Hui Choo , Magee Allan , Wu Guangyu , Paulson Steve , Davies Bill 
Published: November 2013

In designing fixed offshore platforms located in regions of severe wave conditions, the potential resonant response of the hull structure due to wave loads must be checked. Since the natural frequency of vibration of the hull structure is typically much higher than the dominant design wave frequency, conventional wave load analysis based on linear wave theory does not show dynamic amplification. However, it is known that steep waves are nonlinear and may contain significant energy at higher harmonics of the fundamental frequency. When the forcing frequency of the higher-harmonic wave load is close to the natural frequency of the structural vibration, a resonance i.e. ringing will occur and the structural dynamic response will be significantly amplified.
This paper describes an analysis procedure to estimate high-frequency dynamic load on a Gravity Based Structure (GBS) exposed to severe sea states using Computational Fluid Dynamics (CFD) analysis and modal analysis. To fill the statistical gap between the extreme values from short-duration CFD-modal analysis and that from 3-hour design sea states, an approximation method has been developed to estimate the global dynamic load from the measured quasi-static load in earlier model test and to obtain a calibration factor for the CFD-modal analysis results.
Fatigue Assessment of Threaded Segment Specimens Based on the Weakest Link Theory
Authors: Fjeldstad Arne , Wormsen Anders , Kirkemo Finn 
Published: November 2013

In this paper, the weakest link approach has been used to estimate the fatigue life of threaded segment specimens based on fatigue test data of smooth specimens of the same material. The segment specimens are cut outs from an ACME threaded component with a thread geometry typically used in subsea connectors.
Fatigue life estimates of the threaded specimens were also made by means of the local stress approach which is often the prescribed method in standards and recommended practices, such as DNV-RP-C203. This method uses the von Mises stress range at the most severe location of the specimen when estimating the fatigue life.
The estimated S–N curve based on the weakest link approach shows good correspondence with fatigue test results of the threaded segment specimens. The estimated S–N curve based on the local stress approach is well below the S–N curve for the threaded segment specimen. A factor between two and three on stress is observed. Hence, the inherent level of conservatism related to the local stress approach when assessing the fatigue strength of components with very high stress concentration factors is considered to be high.
Effects of the Presence of CO2 at the Well/Caprock Interface: Crystallization Damage
Authors: Manzanal Diego , Pereira Jean-Michel 
Published: November 2013

In the context of CO2 geological storage, it is important to assess the safety and efficiency of the storage operation and thus to prevent CO2 leakage. Most probable leakage paths are constituted by the natural (faults) or artificial (around wells) interfaces.
In this study, the effects of the presence of carbon dioxide on the behaviour of a particular interface are considered. A chemo-poro-mechanical model for the excavated damaged zone located at the interface between the injection well cement and the caprock has been developed. This constitutive model accounts for the precipitation of calcium carbonates coming from the carbonation of the well cement. Crystallisation pressure induced by these carbonates modifies the stress state in the materials at the interface. The model couples a simplified chemistry of carbonates precipitation with a poro-mechanical model accounting for damage of geomaterials due to tensile stress states. This poro-mechanical model is developed at the macroscale but an insight into the material’s microstructure is also included through a description of the material’s pore size distribution and its evolution with crystallisation and damage.
Development of a New Fatigue Testing Machine for High Frequency Fatigue Damage Assessment
Authors: Osawa Naoki , Nakamura Tetsuya , Yamamoto Norio , Sawamura Junji 
Published: November 2013

A new simple fatigue testing machine, which can carry out fast and low-cost fatigue tests of welded joints subject to wave with high frequency vibration, has been developed. This machine is designed for plate bending type fatigue tests, and wave load is applied by using motors with eccentric mass. Springing vibration is superimposed by attaching an additional vibrator to the test specimen, and whipping vibration is superimposed by an intermittent hammering.
Fatigue tests which simulate springing and whipping by a conventional servo-type fatigue testing machines are very expensive and use a large amount of electricity. If one uses these conventional machines, it is difficult to simulate superimposed stress wave forms at high speed, and it takes long hours of testing to examine the high frequency effect. In contrast, it is found that fatigue tests can be carried out in fast, i.e. waves with 10Hz or higher frequency for out-of-plane gusset welded joint specimens with 12mm plate thickness by using the developed machine. The electricity to be used for fatigue tests could be minimal, for example one thousandth of that needed for conventional machines. These results demonstrate the superiority of the developed machine.
Second-Order Kinematics Underneath Irregular Waves
Authors: Birknes Jørn , Hagen Øistein , Johannessen Thomas B. , Lande Øystein , Nestegård Arne 
Published: November 2013

The present paper is concerned with the prediction of horizontal velocities underneath measured irregular wave surface elevations. The simple case of unidirectional waves in deep water is considered. The main challenge in calculating accurately the kinematics in the crest region is related to the treatment of the contribution from wave components with frequencies much higher than the frequencies near the spectral peak. When using linear or weakly nonlinear perturbation methods, the wave components are superimposed at the still water level and it is necessary to truncate the tail of the spectrum in order to calculate accurately the velocity in the crest region.
In the present paper, results from three methods of calculating the crest kinematics are compared with the model test results of Skjelbreia et al. [1]:
• The second-order model of Stansberg et al. [5] which truncates consistently the high frequency part of the spectrum.
• The second-order model of Johannessen [13] which calculates the velocity directly at the instantaneous free surface.
• The Wheeler [3] stretching method which stretches the linear velocity profile from the still water level to the instantaneous free surface.
In addition to comparing the horizontal velocity profiles underneath the crest, time traces of horizontal velocity is compared at the free surface in the vicinity of a large crest. The latter comparison highlights the differences between the models and the challenge of accurate predictions close to top of crest. All three models show a reasonable agreement with model test results although it is clear that the first two methods are superior to the Wheeler method.
Drilling Riser VIV Tests With Prototype Reynolds Numbers
Authors: Lie Halvor , Braaten Henning , Szwalek Jamison , Russo Massimiliano , Baarholm Rolf 
Published: November 2013

For deep-water riser systems, Vortex Induced Vibrations (VIV) may cause significant fatigue damage. It appears that the knowledge gap of this phenomenon is considerable and this has caused a high level of research activity over the last decades. Small scale model tests are often used to investigate VIV behaviour. However, one substantial uncertainty in applying such results is scaling effects, i.e. differences in VIV response in full scale flow and small scale flow. To (partly) overcome this obstacle, a new innovative VIV test rig was designed and built at MARINTEK to test a rigid full scale riser model. The rigid riser model is mounted vertically and can either be elastically mounted or be given a forced motion. In the present version, the cylinder can only move in the cross-flow (CF) direction and is restricted in the in-line (IL) direction.
The paper reports results from a drilling riser VIV experiment where the new rest rig has been used. The overall objective of the work is to study possible VIV suppression to improve operability of retrievable riser systems with auxiliary lines by adding riser fins. These fins are normally used as devices for protection of the auxiliary lines.
The test program has recently been completed and analysis is an on-going activity. However, some results can be reported at this stage and more results are planned to be published.
A bare riser model was used in a Reynolds number (Rn) scaling effect study. The riser model was elastically mounted and towed over a reduced velocity range around 4 – 10 in two different Rn ranges, 75 000 – 192 000 (subcritical regime) and 347 000 – 553 000 (critical regime). The difference in the displacement amplitude to diameter ratio, A/D, is found to be significant.
The elastically mounted riser was also towed with various drilling riser configurations in order to study VIV/galloping responses. One configuration included a slick joint riser model with 6 kill & choke lines; another has added riser fins too. The riser model is based on a specific drilling riser and the kill and choke lines have various diameters and have a non-symmetrical layout.
The various riser configurations have also been used in forced motion tests where the towed model has been given a sinusoidal CF motion. Forces have been measured. Determination of the force coefficients is still in progress and is planned to be reported later.
Scaling effects appear to be a significant uncertainty and further research on the subject is recommended.
The slick joint drilling riser configuration generally increased the displacements compared to displacements of the bare riser model. The drilling riser configuration with protection fins, kill and choke lines generally reduced the displacements compared to displacements of the bare riser model. For both riser systems, tests showed that the response is sensitive to the heading of the current.
Incidence Density of Invasive Fungal Infections during Primary Antifungal Prophylaxis in Newly Diagnosed Acute Myeloid Leukemia Patients in a Tertiary Cancer Center, 2009 to 2011
Authors: Gomes Marisa Z. R. , Mulanovich Victor E. , Jiang Y. , Lewis Russell E. , Kontoyiannis Dimitrios P. 
Published: November 2013

ABSTRACT

Although primary antifungal prophylaxis (PAP) is routinely administered in patients with acute myeloid leukemia (AML) during remission-induction and consolidation chemotherapy, the impact of PAP on the incidence of invasive fungal infections (IFIs) is not well described. We retrospectively analyzed the incidence of IFIs in 152 patients with AML who had been admitted to a tertiary cancer center between August 2009 and March 2011 and received PAP within 120 days after first remission-induction chemotherapy. We excluded patients who had undergone stem cell transplantation. Patients received a PAP drug with anti-
Aspergillus
activity during 72% (7,660/10,572) of prophylaxis-days. The incidence of documented IFIs (definite or probable according to revised European Organization for Research and Treatment of Cancer [EORTC] criteria) was 2.0/1,000 prophylaxis-days (95% confidence interval [CI], 1.23 to 3.04). IFIs due to molds were more common than IFIs due to yeasts (1.5/1,000 prophylaxis-days versus 0.4/1,000 prophylaxis-days;
P
= 0.01). Echinocandin-based PAP (8.6 and 7.1/1,000 prophylaxis-days, respectively) was associated with higher rates of documented IFIs than anti-
Aspergillus
azoles (voriconazole or posaconazole) (2.4 and 1.1/1,000 prophylaxis-days, respectively) at both 42 days (
P
= 0.03) and 120 days (
P
< 0.0001) after first remission-induction chemotherapy. The incidence of overall (documented and presumed) IFIs (
P
< 0.001), documented IFIs (
P
< 0.01), and empirical antifungal therapies (
P
< 0.0001) was higher during the first 42 days than after day 42. Despite the broad use of PAP with anti-
Aspergillus
activity, IFIs, especially molds, remain a significant cause of morbidity and mortality in AML patients, predominantly during the remission-induction phase. Patients receiving echinocandin-based PAP experienced higher rates of IFIs than did those receiving anti-
Aspergillus
azoles.