bluuebunny/crossref_metadata_2025 huggingface dataset:
Alzheimer's disease beyond the genomic era: nuclear magnetic resonance (NMR) spectroscopy‐based metabolomics
Authors: Barba Ignasi , Fernandez‐Montesinos Rafael , Garcia‐Dorado David , Pozo David
Published: June 2008

Introduction

Rationale for metabolomics in Alzheimer's disease

Metabolomics of Alzheimer's disease

Methodology: NMR metabolomics at work

Conclusions

Alzheimer's disease (AD) is a complex disease, with no definitive biomarkers available that allow clinical diagnosis; this represents a major problem for the advance of efficient drug discovery programs. A successful approach towards the understanding and treatment of AD should take into consideration this complex nature. In this sense, metabolic networks are subject to severe stoichiometric restrictions. Metabolomics amplifies changes both in the proteome and the genome, and represents a more accurate approximation to the phenotype of an organism in health and disease. In this article, we will examine the current rationale for metabolomics in AD, its basic methodology and the available data in animal models and human studies. The discussed topics will highlight the importance of being able to use the metabolomic information in order to understand disease mechanisms from a systems biology perspective as a non‐invasive approach to diagnose and grade AD. This could allow the assessment of new therapies during clinical trials, the identification of patients at risk to develop adverse effects during treatment and the final implementation of new tools towards a more personalized medicine.
Endogenous anti‐inflammatory neuropeptides and pro‐resolving lipid mediators: a new therapeutic approach for immune disorders
Authors: Anderson Per , Delgado Mario
Published: June 2008

Introduction

Tuning immune tolerance with anti‐inflammatory neuropeptides

Resolution of inflammation by endogenous lipid mediators

Therapeutic perspectives: rationale for using endogeneous neuropeptides and lipid mediators in immune disorders

Identification of the factors that regulate the immune tolerance and control the appearance of exacerbated inflammatory conditions is crucial for the development of new therapies of inflammatory and autoimmune diseases. Although much is known about the molecular basis of initiating signals and pro‐inflammatory chemical mediators in inflammation, it has only recently become apparent that endogenous stop signals are critical at early checkpoints within the temporal events of inflammation. Some neuropeptides and lipid mediators that are produced during the ongoing inflammatory response have emerged as endogenous anti‐inflammatory agents that participate in the regulation of the processes that ensure self‐tolerance and/or inflammation resolution. Here we examine the latest research findings, which indicate that neuropeptides participate in maintaining immune tolerance in two distinct ways: by regulating the balance between pro‐inflammatory and anti‐inflammatory factors, and by inducing the emergence of regulatory T cells with suppressive activity against autoreactive T‐cell effectors. On the other hand, we also focus on lipid mediators biosynthesized from ω‐3 and ω‐6 polyunsaturated fatty‐acids in inflammatory exudates that promote the resolution phase of acute inflammation by regulating leucocyte influx to and efflux from local inflamed sites. Both anti‐inflammatory neuropeptides and pro‐resolving lipid mediators have shown therapeutic potential for a variety of inflammatory and autoimmune disorders and could be used as biotemplates for the development of novel pharmacologic agents.
The effectiveness of peer support groups in psychosis: a randomized controlled trial
Authors: Castelein S. , Bruggeman R. , Van Busschbach J. T. , Van Der Gaag M. , Stant A. D. , Knegtering H. , Wiersma D.
Published: June 2008

Objective:  To investigate the effect of a (minimally) guided peer support group (GPSG) for people with psychosis on social network, social support, self‐efficacy, self‐esteem, and quality of life, and to evaluate the intervention and its economic consequences.

Method:  In a multi‐center randomized controlled trial with 56 patients in the peer support group and 50 patients in the control condition, patients were assessed at baseline and after the last meeting at 8 months.

Results:  The experimental group showed GPSG to have a positive effect on social network and social support compared with the control condition. In the experimental condition, high attenders favored over low attenders on increased social support, self‐efficacy, and quality of life. Economic evaluation demonstrated groups to be without financial consequences. The GPSG‐intervention was positively evaluated.

Conclusion:  Peer support groups are a useful intervention for people suffering from psychosis by improving their social network.
Exploring the relative influence of biotic interactions and environmental conditions on the abundance and distribution of exotic brown trout (Salmo trutta) in a high mountain stream
Authors: Budy P. , Thiede G. P. , McHugh P. , Hansen E. S. , Wood J.
Published: June 2008

Abstract – In the Logan River, UT, USA, exotic brown trout demonstrate a strong allopatric distribution and occur at high densities at low‐elevation sites and in tributaries, and in low densities at native trout dominated, high‐elevation sites. Summer temperatures and discharge do not appear limiting for growth; adult growth rates were high overall and were greatest when fish were held experimentally at high elevation where they do not occur naturally. Brown trout are superior competitors; competition for space or food was stronger with their own con‐specifics than with other species. Evidence of density dependence was not observed at the juvenile life stage; no consistent relationships were detected between brown trout density and age‐1 condition or lagged, age‐0 weight (g). In contrast, adult brown trout demonstrated density‐dependent effects on condition and growth when reared experimentally. Field estimates of adult growth rates (g·day−1), although variable, declined subtly with increasing density, and annual survival was significantly greater in the mainstem sites (mean = 52%) relative to a high‐density tributary site (mean = 22%). Annual predicted age‐0 brown trout growth potential was four‐times greater at the lowermost site, compared with the highest elevation site, although fish lost weight over winter months at all sites. While adult density dependence may influence population abundance at some sites, extreme spring–winter conditions may ultimately limit the upper elevational extent of brown trout in this system. With changing climatic conditions and the potential for habitat degradation in the future, these results have important implications for native fish conservation.
Brassinin oxidase, a fungal detoxifying enzyme to overcome a plant defense – purification, characterization and inhibition
Authors: Pedras M. S. C. , Minic Zoran , Jha Mukund
Published: June 2008

Blackleg fungi [Leptosphaeria maculans (asexual stage Phoma lingam) and Leptosphaeria biglobosa] are devastating plant pathogens with well‐established stratagems to invade crucifers, including the production of enzymes that detoxify plant defenses such as phytoalexins. The significant roles of brassinin, both as a potent crucifer phytoalexin and a biosynthetic precursor of several other plant defenses, make it critical to plant fitness. Brassinin oxidase, a detoxifying enzyme produced by L. maculans both in vitro and in planta, catalyzes the detoxification of brassinin by the unusual oxidative transformation of a dithiocarbamate to an aldehyde. Purified brassinin oxidase has an apparent molecular mass of 57 kDa, is approximately 20% glycosylated, and accepts a wide range of cofactors, including quinones and flavins. Purified brassinin oxidase was used to screen a library of brassinin analogues and crucifer phytoalexins for potential inhibitory activity. Unexpectedly, it was determined that the crucifer phytoalexins camalexin and cyclobrassinin are competitive inhibitors of brassinin oxidase. This discovery suggests that camalexin could protect crucifers from attacks by L. maculans because camalexin is not metabolized by this pathogen and is a strong mycelial growth inhibitor.
Reducing emotional distress in nurses using cognitive behavioral therapy: A preliminary program evaluation
Authors: BRUNERO Scott , COWAN Darrin , FAIRBROTHER Greg
Published: June 2008

Introduction:  Workplace stress among nurses has been associated with high absenteeism, low work satisfaction, and poor retention rates.

Aim:  This pilot study evaluated the effectiveness of a 1 day stress management program on nurses' stress levels.

Methods:  The nurse participants attended an 8 h face‐to‐face interactive workshop based on cognitive behavioral therapy. The subjects also were given a self‐directed manual with reading and exercises to use after the workshop. The nurses were assessed at baseline and at 6 weeks postworkshop attendance using the Nurse Stress Scale (NSS). They were asked to rate their level of stress at work, outside of work, and their overall stress. The participants also were asked to evaluate the perceived usefulness of the workshop at follow‐up.

Results:  The sample consisted of 18 new graduate nurses halfway through their first year. The NSS subscales “nurse–doctor conflict”, “death and dying”, and “nurse–nurse conflict” showed statistically significant improvement at follow‐up. The ratings of stress at work, outside of work, and the overall stress also showed statistically significant improvement.

Conclusions:  The workshop was well‐received by the new graduate nurses. The pre/post findings suggest a beneficial effect of the intervention. The authors are encouraged by the results and now plan to conduct a multisite, randomized controlled trial to seek to establish a wider evidence base for the intervention.
Share Repurchase Offers and Liquidity: An Examination of Temporary and Permanent Effects
Authors: Nayar Nandkumar , Singh Ajai K. , Zebedee Allan A.
Published: June 2008

Open‐market repurchase programs do not allow for precise estimates of share buy‐back intensity to measure liquidity effects. To circumvent the uncertainty surrounding the quantity and timing of shares truly acquired in repurchase programs and to measure their long‐term impact, we examine Dutch auctions and fixed‐price tender offers. We investigate both the temporary and permanent liquidity effects of share repurchase programs and find that the improvement in liquidity is transitory and limited to the tender period when the firm's offer to repurchase shares is outstanding. Improvements in liquidity over longer intervals appear to be the result of an overall price improvement and a reduction in volatility rather than the result of structural change in market dynamics.
Tax‐Adjusted Discount Rates with Investor Taxes and Risky Debt
Authors: Cooper Ian A. , Nyborg Kjell G.
Published: June 2008

This paper derives a tax‐adjusted discount rate formula with a constant proportion leverage policy, investor taxes, and risky debt. The result depends on an assumption about the treatment of tax losses in default. We identify the assumption that justifies the textbook approach of discounting interest tax shields at the cost of debt. We contrast this with an alternative assumption that leads to the

Sick (1990)

result that these should be discounted at the riskless rate. These two approaches represent polar cases. Each generates its results by using a different simplifying assumption, and we explain what determines the correct treatment in practice. We also discuss implementation of the valuation procedure using the capital asset pricing model.
Predicting susceptibility to future declines in the world's frogs
Authors: Bielby Jon , Cooper N. , Cunningham A.A. , Garner T.W.J. , Purvis A.
Published: June 2008

The 2004 Global Amphibian Assessment demonstrated that almost 400 anuran species have recently moved closer to extinction due to a host of threat mechanisms. Of particular concern is the role of the fungal pathogen, Batrachochytrium dendrobatidis (Bd), for which more traditional conservation management is not effective. Determining which biological and environmental factors affect a species' susceptibility to these mechanisms would greatly aid conservation prioritisation and planning. We performed phylogenetic comparative analyses to determine which biological and environmental factors predict species' susceptibility to rapid declines, both generally and in the context of Bd. Our results extend the findings of previous finer scale studies: we find that high‐altitude, restricted‐range, aquatic species with low fecundity are most likely to suffer Bd‐related declines. We use our findings to identify those species most at risk of Bd‐related declines and global extinction in the future, and identify areas where many species are predicted to be susceptible. Identifying susceptible species in advance of their decline is particularly important in setting priorities when, as here, declines are hard to arrest once underway.
Toward a biocultural theory of avoided extinction
Authors: Ladle Richard J. , Jepson Paul
Published: June 2008

Avoiding extinction is one of the main aims of the global conservation movement and its study has historically been dominated by ecological thinking about the consequences of small population size and the identification of the proximate causes of population decline. Here we argue that any successful theorization on avoiding extinction has to look beyond ecology to incorporate the behavior of conservationists, conservation organizations, and other societal actors. We develop a “biocultural” framework based on a typology of extinction that emphasizes the different meanings and power of the term and discuss how these might inform more effective global conservation policy and practice. Seen through a biocultural perspective, we argue that extinction will only be effectively reduced when scientific evidence, cultural frames, institutional frameworks, and organizational interests align.
Oxidative stress and hippocampus in a low‐grade hepatic encephalopathy model: protective effects of curcumin
Authors: Roselló Diego Martín , Balestrasse Karina , Coll Carlos , Coll Sebastian , Tallis Silvina , Gurni Alberto , Tomaro María Lujan , Lemberg Abraham , Perazzo Juan Carlos
Published: June 2008

Aim:  The present study was performed on prehepatic portal hypertensive rats, a model of low‐grade hepatic encephalopathy, designed to evaluate whether oxidative stress was a possible pathway implicated in hippocampal damage and if so, the effect of an anti‐oxidant to prevent it.

Methods:  Prehepatic portal hypertension was induced by a regulated portal vein stricture. Oxidative stress was investigated by assessing related biochemical parameters in rat hippocampus. The effect of the anti‐oxidant curcumin, administered in a single i.p. dose of 100 mg/kg on the seventh, ninth and eleventh days after surgery, was evaluated.

Results:  Oxidative stress in the rat hippocampal area was documented. Curcumin significantly decreased tissue malondialdehyde levels and significantly increased glutathione peroxidase, catalase and superoxide dismutase activities in the hippocampal tissue of portal hypertensive rats.

Conclusion:  Oxidative stress was found to be implicated in the hippocampal damage and curcumin protected against this oxidative stress in low‐grade hepatic encephalopathic rats. These protective effects may be attributed to its anti‐oxidant properties.
Dynamics of Coupled Oscillators Excited by Dry Friction
Authors: Pascal Madeleine
Published: June 2008

In this paper, we present an analytical method to investigate the behavior of a two-degree-of-freedom oscillator excited by dry friction. The system consists of two masses connected by linear springs. These two masses are in contact with a driving belt moving at a constant velocity. The contact forces between the masses and the belt are obtained assuming Coulomb’s friction law. Two families of periodic motions are found in closed form. The first one includes stick-slip oscillations with two switches per period, the second one is also composed of stick-slip motion, but includes three switches per period. In both cases, the initial conditions and the time duration of each kind of motions (stick or slip phases) are obtained in analytical form.
A Runback Criterion for Water Drops in a Turbulent Accelerated Boundary Layer
Authors: White Edward B. , Schmucker Jason A.
Published: June 2008

Predicting the runback threshold for liquid drops in aerodynamic boundary layers is a challenging problem with numerous applications including aircraft icing simulations. The critical parameters that govern drop runback are investigated in this experiment by using a wind tunnel that provides a turbulent accelerated flow similar to flows near an unswept wing’s leading edge. The experiments feature water drops on aluminum with a contact angle of 70±5deg. Results show that significant water∕air interface unsteadiness precedes drop runback. This is likely due to air-flow separation in the drop wakes. For displacement-thickness-scaled Reynolds numbers ranging from 348 to 429, a constant-Weber-number runback threshold We=3.45±0.09 is found to adequately correlate the runback results.
Effervescent Atomization of Viscoelastic Liquids: Experiment and Modeling
Authors: Geckler S. C. , Sojka P. E.
Published: June 2008

The effervescent atomization of viscoelastic liquids is reported. A total of 23 fluids, formulated from a 60wt% glycerine/40wt% water solvent to which were added varying concentrations (0.001–0.5wt%) of poly(ethylene oxide) polymers whose molecular weights ranged from 12,000 to 900,000, were sprayed through a conventional effervescent atomizer. Mean drop sizes were measured using a forward light scattering instrument. The drop size (D32) data show the expected decrease with an increase in air-liquid ratio by mass (ALR), the expected increase with an increase in polymer concentration, plus an increase with an increase in polymer molecular weight for most cases. However, no significant change in D32 was observed for polymer solutions whose molecular weights ranged from 12,000 to 35,000, suggesting the presence of a critical molecular weight below which spray performance is unaltered. This argues for two different factors controlling drop size: Polymer molecular weight is most influential at the highest polymer concentrations while polymer concentration is most influential at the lowest polymer concentrations. Analysis of the spray formation process was carried out using a ligament formation model previously developed for the effervescent atomization of Newtonian liquids coupled with a linear stability model for the breakup of viscoelastic liquid jets. The jet breakup model assumes that an unrelaxed axial tension exists within the fluid. A comparison of model predictions and experimental data indicates that the model predicts the observed dependencies of mean drop size on ALR, polymer concentration, and polymer molecular weight. Quantitative agreement is within 10–50% of experimental values in all cases. Finally, a shortcoming of the model is noted and a means of avoiding this limitation reported.
Three-Dimensional Analytical Simulation of Flexible Pipe Wall Structure
Authors: McNamara J. F. , Harte A. M.
Published: June 2008

A three-dimensional analytical model of the mechanical response of a bonded layered flexible pipeline section to a general set of loads and pressures is presented. Stiffness relations for isotropic, orthotropic and helically wound armoring layers are developed and combined to form a total section stiffness equation incorporating inter-layer pressures and radial deformations. These layers may be used to model the mechanical responses of flexible pipelines including any number and order of layers. Typical loads are taken from a three-dimensional analysis of a flexible production riser in a steep-wave configuration in 310 m water depth. An illustrative pipe section with five layers, including an inner steel tube, two contrawound steel cable layers and two modeled with rubber matrix materials, is subjected to this three-dimensional load set. Computations show the dominant influence of the steel strands in carrying the ambient loads and also gives an accurate picture of the radial distribution of inter-layer pressures across the pipe thickness. The analytical model is designed to give a detailed assessment of deformations and stresses in the various layers such that estimates may be made of critical parameters including wear, slip, rupture, debonding and other related aspects of flexible pipe performance.
Drag Force on Cylinders Oscillating at Small Amplitude: A New Model
Authors: Anaturk A. R. , Tromans P. S. , van Hazendonk H. C. , Sluis C. M. , Otter A.
Published: June 2008

A new semi-empirical model is derived for calculations of hydrodynamic damping (or drag) forces on smooth or rough cylinders oscillating at small amplitude and high frequency. This model covers the attached flow regime where the conventional Morison’s equation fails to simulate the drag forces acting on circular cylinders. It involves the calculation of the energy dissipated in the boundary layer on the cylinder surface. The empirical input data for the model are amplitude and phase of the wall shear stresses on the cylinder. The model is verified against fluid force measurements from a test tank and published data. These experiments were carried out at small-amplitude / high-frequency with smooth and rough circular cylinders. Data from the literature is also included for verification. Results from the present work can be used to estimate hydrodynamic damping forces for the analysis of jack-up response around resonant frequency. Other applications are dynamic behavior of jackets during installation, SALMs, TLPs and risers.
An Efficient Numerical Method for Calculating the Statistical Distribution of Combined First-Order and Wave-Drift Response
Authors: Naess A. , Johnsen J. M.
Published: June 2008

The paper describes an efficient and accurate numerical procedure for calculating the probability distribution function of combined first-order and slowly varying, second-order hydrodynamic loads and response of compliant offshore structures. No approximations are made except those inherent in the numerical calculations. The method does not require extensive computer capacity; in fact it can be implemented on any standard PC. Several example calculations serve to illustrate the method, and its accuracy is demonstrated by comparison with cases where exact analytical results are available. The accuracy of previously proposed approximations are also discussed.
Wire Stress Calculations in Helical Strands Undergoing Bending
Authors: Raoof M. , Huang Y. P.
Published: June 2008

Steel cables play an important role in many offshore applications. In many cases, an understanding of the magnitude and pattern of bending stresses in the individual component wires of a bent strand is essential for minimizing the risk of their failure under operating conditions. Following previously reported experimental observations, a theoretical model is proposed for obtaining the magnitude of wire bending stresses in a multi-layered and axially preloaded spiral strand fixed at one end and subsequently bent to a constant radius of curvature. The individual wire bending stresses are shown to be composed of two components. The first component is the axial stress generated in the wires due to interwire/interlayer shear interactions between the wires in a bent cable, and the second component is associated with the wires bending about their own axes. Using the theoretical model, which includes the effects of interwire friction, parametric studies on a number of realistic helical strands with widely different cable (and wire) diameters and lay angles subjected to a range of practical mean axial loads, and subsequently bent to a range of radii of curvature with one end of the cable fixed against rotation, have been carried out. It is shown that for most practical applications, the axial component of wire stresses due to friction is much greater than the second component of bending stresses associated with the individual wires bending about their own axes.
Hydrodynamic Forces on Pipelines: Model Tests
Authors: Bryndum M. B. , Jacobsen V. , Tsahalis D. T.
Published: June 2008

An extensive model test program on the hydrodynamic forces on a submarine pipeline resting on the sea bottom and exposed to steady current, regular waves, combined steady current and regular waves, irregular waves, and combined steady current and irregular waves has been performed. The hydrodynamic forces in both the in-line and the cross-flow directions have been analyzed using three different methods, i.e., least-squares-fit analysis based on Morison-type equations, Fourier analysis, and maximum force analysis. The force coefficients associated with each method have been determined for a wide range of environmental conditions. The results of the tests are presented in terms of the calculated force coefficients and their dependence on various nondimensional parameters is discussed. Furthermore, comparisons with other test data are presented.
An Investigation of Hydrodynamic Damping of Vertical Bottom-Pivoted Cylinders
Authors: Haritos N. , Yang H.
Published: June 2008

This paper investigates theoretical formulations for the radiation and “drag”-dependent hydrodynamic damping mechanisms for vertical bottom-pivoted cylinders under excitation by irregular uni-directional Pierson-Moskowitz waves. Experimental verification of the coexistence of these two forms of hydrodynamic damping is provided from the results of a program of research being conducted in the Michell Laboratory at the University of Melbourne on a wide range of cylinder test conditions.
Elastic-Plastic Fracture at Surface Flaws in HSLA Steel Weldments
Authors: Read D. T. , Petrovski B. I.
Published: June 2008

The combined effects of weld-strength-mismatch and crack size on strength and ductility were studied experimentally using tensile panels. Two high-strength, low-alloy steel base metals were welded with two different electrodes to produce a specimen matrix which contained one each of undermatched, normal-matched, and overmatched welds and one base metal. Two nominal crack sizes were used in two different locations, the weld center and the heat-affected-zone. The basic observable quantities were the strength and ductility of the tensile panels. Measurements of the applied J-integral were performed by instrumenting a contour on the specimen surface with strain gages. It was demonstrated that cracks reduce weld strength in proportion to their area, but that their effect on ductility can be much larger, far out of proportion to the crack area. Overmatched welds were observed to shield cracks from plastic strains when the cracks had a relative area of about 2.5 percent of the cross section; but this effect was lost for cracks with a relative area of 12.6 percent. The J-integral measurements indicated that the differences in behavior among the various weld-strength-mismatch conditions could be explained by the applied J-integral, without the need to invoke differences in fracture resistance. The measured values of fracture resistance, in units of J-integral and crack-mouth-opening-displacement, were comparable for three-point-bend specimens of all the specimen types.
Modeling Procedures for the Stress Analysis of Flexible Pipe Cross Sections
Authors: Harte A. M. , McNamara J. F.
Published: June 2008

Thick tube theory is incorporated into an existing analytical model for the three-dimensional analysis of bonded flexible pipe cross sections under offshore loading conditions. The original model considers material layers as isotropic/orthotopic thin tubes, and layers of helically wound reinforcing cables are modeled separately. The improvement in the results obtained with the incorporation of the new thick tube layer is demonstrated for a flexible pipe with D/t = 10. The finite element technique has also been used to model this type of pipe structure. Pipe sections are discretized using axisymmetric elements for the tube-type layers and special discrete reinforcement elements for the helical cables. A particular example of a three-layer doubly reinforced pipe section under internal pressure is studied. Good agreement is found between analytical model and finite element results for all the main deformation and stress quantities including cable stresses.
Prediction of Residual Stresses and Distortions in Welded Structures
Authors: Josefson B. L.
Published: June 2008

A good knowledge of the welding residual stress field and the corresponding distortion is needed when the interaction between manufacturing stresses and future (mechanical and/or thermal) design loads is studied, for example, with respect to possible crack initiation and growth in the HAZ, and also with respect to buckling. It is proposed here that a qualitatively good estimate of the welding residual stresses can be obtained by using FEM without following the temperature history during welding and cooling in detail. The procedure proposed is applied to two different problems: multi-pass butt welding of pipes, and spot welding of box beams. For the case of multi-pass butt welding of pipes, experimental results are available and a good agreement with these results is observed.
Thickness Effect Criterion for Fatigue Strength Evaluation of Welded Steel Structures
Authors: Yagi J. , Machida S. , Matoba M. , Tomita Y. , Soya I.
Published: June 2008

From a practical point of view, some measures to reduce the thickness effect backed by a reasonable criterion are required for fabricating structures with heavy section plates. In this study, the thickness effect was investigated by systematic experiments on welded steel joints with thicknesses ranging from 10 to 80 mm. Cruciform joints and T-joints with improved weld by overall profiling or toe-grinding were tested under pulsating tension and under pulsating bending, respectively. These experimental results were analyzed together with the previous results of as-welded joints. As a result, it was concluded that the thickness effect exponents for various conditions may be classified into three categories according to the combination of joint type and loading mode. As-welded joints under bending stress have the steepest thickness effect exponent of −1/3, while as-welded joints under tension with an exponent of −1/5 is milder in thickness effect than that specified in the existing codes. If the weld profile is improved by grinding, the thickness effect becomes much milder to an exponent of −1/10. The as-weld joints with constant-sized attachments also have an exponent of −1/10. Furthermore, thickness effect dependence on fatigue life and thickness effect under random stress were investigated. Based on these results, this study proposes a new evaluation criterion for design purposes.
Heat-Affected Zone Fracture Toughness of 420–500-MPa Yield Strength Steels: Effects of Chemical Composition and Welding Conditions
Authors: Tronskar J. P.
Published: June 2008

During the last five years, high-strength steels with yield strengths in the range 420 to 500 MPa have attracted considerable interest within the offshore industry, primarily due to the potential for weight saving and reduction in volume of weld metal through the use of reduced section thicknesses. With respect to chemical composition these steels are developed following much the same philosophoy as for the modern normalized structural steels. Due to the increased stress level in these higher strength steels, it is anticipated that brittle fracture initiation occurring in the coarse-gained HAZ will be more critical for these steels than for the lower strength normalized grades. The objective of this paper is to present the results from several experimental investigations carried out at VERITEC during the last five years to study the factors affecting the crack tip opening displacement (CTOD) fracture toughness of the heat-affected zone (HAZ) in structural steels in the yield strength range 420–500 MPa. Typical CTOD fracture toughnesses of the HAZ in normalized 350-MPa yield strength steels used in offshore structures are also presented for comparison. The results of the investigations confirm that the same chemical compositional factors which are known to influence the HAZ fracture toughness of normalized steels are also important for the 420–500-MPa yield strength steels. It is demonstrated that the width of the HAZ is important for the initiation of brittle fracture of pop-in and that this width must exceed a certain minimum value for such events to occur. For different welding conditions, i.e., welding currents/travel speeds, the width of the coarse-grained HAZ changes considerably along the periphery of the weld bead. Thus, one may obtain widely differing results depending on the exact fatigue pre-crack placement. In addition to the weld cooling time between 800 and 500° C, Δt8/5 and the retention time above 1000° C during the weld thermal cycle, RT1000, the welding process and consumables also exert a strong influence on the CTOD values of the coarse-grained HAZ.
The Compressive Strength of Ice Cubes of Different Sizes
Authors: Kuehn G. A. , Schulson E. M. , Jones D. E. , Zhang J.
Published: June 2008

Cubes of side length from 10 to 150 mm were prepared from freshwater granular ice of about 1 mm grain size and then compressed uniaxially to failure at −10° C. In addition to size, the variables were strain rate (10−5s−1 and 10−2s−1) and boundary conditions (ground brass plates, ground and polished brass plates, and brass brushes). The results showed that over the range investigated, size is not an important factor when considering the ductile compressive strength of ice. It also appears that size is not a factor when considering the brittle compressive failure strength under more ideal loading conditions. However, under less ideal conditions where perturbations on the loading surface may be significant, the brittle compressive strength decreases as the size of cube increases. In this case, the effect is attributed to nonsimultaneous failure.
Risk Analysis and Risk Management for Offshore Platforms: Lessons From the Piper Alpha Accident
Authors: Pate´-Cornell M. E.
Published: June 2008

A probabilistic risk analysis (PRA) framework is used to identify the accident sequence of the 1988 Piper Alpha accident. This framework is extended to include the human decisions and actions that have influenced the occurrences of these basic events, and their organizational roots. The results of this preliminary analysis allow identification of a wide spectrum of possible risk reduction measures, ranging from classical technical solutions such as addition of redundancies, to organizational improvements such as a change in the maintenance procedures. An explicit PRA model is then developed to assess the benefits of some of these safety measures based, first, on the original contribution to the overall risk of the failure modes that these measures are designed to avert, and second, on the degree to which they can reduce the probabilities of these failure modes. PRA can then be used as a management tool, allowing optimization of risk management strategies based both on the qualitative information about causalities provided by the accident, and on the quantitative information about failure probabilities updated in the light of new events. It is shown how PRA can be used to assess, for example, the cost-effectiveness of safety measures designed to decrease the probability of severe fire damage onboard platforms similar to Piper Alpha.
Current-Induced Fluidelastic Instabilities of a Multi-Tube Flexible
Riser: Theoretical Results and Comparison With Experiments
Authors: Price S. J. , Pai¨doussis M. P. , Al-Jabir A. M.
Published: June 2008

Previous experiments on a five-riser cluster in steady cross-flow have indicated that for certain orientations of the cluster the peripheral, or wing, risers can undergo violent flow-induced vibrations. It was shown that these vibrations were not due to vortex shedding; furthermore, it was suggested that they are due to a classical self-excited fluidelastic instability. In the present paper, a previously developed quasi-steady fluidelastic stability analysis for a group of circular cylinders in steady crossflow is modified to enable the stability of a flexible riser in a five-riser bundle to be analyzed. As input to the theoretical model, the static fluid force coefficients on a peripheral riser, and the manner in which they vary with displacement, are required. These were measured for a number of orientations of the cluster with respect to the free-stream current, using a wind tunnel model. Using this data in the analysis, the stability of a five-riser cluster was investigated. Instability is predicted to occur for the same orientations of the riser as obtained from the experimental results; however, the quantitative agreement between experimental and theoretical critical flow velocities for instability to occur is not as good. Theory also predicts the system to be stable for those orientations where no instability was obtained experimentally.
Tubular Conical Columns for Offshore Structures
Authors: Cox S. J.
Published: June 2008

We examine submerged nonlinear tubular columns with slenderness ratios between 40 and 160 and ratios of diameter to thickness between 20 and 50. We demonstrate that the column’s Euler buckling load can be increased nearly 30 percent by a volume preserving taper of only a few degrees. We determine the effect of hydrostatic pressure and self-weight on such conical columns and offer some preliminary remarks on the role played by model imperfections.
Fracture of Surface-Cracked Undermatched Weld Joint in High-Strength
Steel
Authors: Petrovski B. , Kocak M.
Published: June 2008

The objective of this paper is to study the combined effects of weld metal undermatching and crack location on the fracture behavior of transversely loaded butt-welded joints in high-strength steel. Surface-cracked tensile panels were instrumented with stain gages and tested with notch locations at the heat-affected zone (HAZ), base and 30 percent undermatched weld metals. It can be expected that for a given applied strain, the level of the strain concentration developed in undermatched weld region will be significantly lower in the high strain-hardening welds compared to the low work-hardening weld joint in high-strength steels. Therefore, in higher strength steel undermatched welds, substantial increase of the strain accumulation should be expected. Detailed strain measurements and tensile panel tests of this study reveal that if there is a defect in the undermatched weld, a combination of the low weld metal toughness and resulting strain accumulation in the weld metal lead to poor fracture performance. The HAZ notched tensile panel results indicate that weld metal undermatching causes an unsymmetrical strain distribution at the crack vicinity. Despite the occurrence of the high applied strain concentration at the weld metal side of HAZ notched panel, the gross section yielding (GSY) occurred similar to the base metal notched one. On the other hand, weld metal notched panels showed net section yielding (NSY) with a considerably reduced ductility. An important difference in 30 percent undermatched weld joint fracture performance, however, emerges when results are analyzed in terms of crack growth resistance curves. The J R-curves of the HAZ and weld metal notched panels have shown lower resistance behavior compared to the base metal panel. Therefore, it is concluded that the fracture performance of the undermatched welds cannot be fully understood if only strength or total strain capacity (applied side) of the entire panel is considered. The fracture toughness (material resistance side) of the undermatched weld joint should also be an integral part of the fracture performance assessment procedure.
Evaluation of Uncertainties in Loadings on Offshore Structures due to
Extreme Environmental Conditions
Authors: Bea R. G.
Published: June 2008

This paper summarizes results from a Canadian Standards Association (CSA) sponsored study of the uncertainties associated with extreme (1000 to 10,000-yr return periods) environmental loadings acting on offshore structures (Bea, 1991). The evaluations of the loadings addressed loading effects that resulted from dynamic and nonlinear interactions of the structures. Loading uncertainties were organized and characterized in two categories: 1) inherent randomness (aleatory uncertainty), and 2) analytical variability (epistemic uncertainty). The study addressed the global ultimate limit state performance of three structures designed according to the provisions of the draft CSA guidelines (1989a, 1989b) for offshore structures: 1) a concrete Gravity Base Structure (GBS) located off the East coast of Canada (Hibernia), 2) a steel pile template located on the Scotian Shelf off Sable Island, and 3) a caisson retained island located in the Mackenzie Delta area of the Beaufort Sea (Amuligak). The results of this study indicate that, based on presently available information and data, it is often not possible to develop unambiguous characterizations of uncertainties. The different technical communities that background environmental conditions and forces (storms, earthquakes, ice) recognize and integrate these uncertainties into loading characterizations in different ways. In many cases, major sources of uncertainty are not included in probabilistic characterizations. Because of the needs for design code information sensitivity and consistency in demonstrating compliance with target reliability goals, there is a need for well-organized and definitive evaluations of uncertainties in extreme environmental loadings and load effects (Bitner-Gregersen et al., 1993).
A Finite Element Model for Cables With Nonsymmetrical Geometry and Loads
Authors: Le T. T. , Knapp R. H.
Published: June 2008

A new two-dimensional finite element model is proposed for the deformation analysis of cable cross sections. The deformations of the cable cross section are of considerable design interest because of their effect on the induced torque or rotation of the cable. This model accounts for material orthotropy and nonsymmetrical geometry and loads. Each component of the cable is assumed to possess a circular cross section and is modeled as a macro-element having nodal degrees-of-freedom at all contact points with adjoining components. Usual finite element procedures are applied to solve for the unknown displacements at contact nodal points. The model is implemented in a computer code and is verified by test results obtained for an as-built cable.
Critical Assessment of the Least Square Error Method Used in Derivation of Morison’s Force Coefficients
Authors: Najafian G. , Burrows R.
Published: June 2008

The least square error (LSE) method is frequently used in determination of Morison’s coefficients from the analysis of measured wave forces on circular cylinders. It will be proved in this paper that Morison’s coefficients determined from the LSE method always lead to predicted forces which have smaller variances (2nd-order statistical moments) than those of the measured forces. In other words, it is proved that predicted forces from this method are of lower intensity compared to the measured forces, and hence can be unconservative. A new method, termed the maximum correlation (MC) method, has been introduced. This method has all the advantages of the LSE method, but leads to predicted forces whose variances are equal to those of the measured forces.
Stochastic Storm Profiles for Strain Accumulation in Clay
Authors: Ronold K. O. , Winterstein S. R.
Published: June 2008

For offshore gravity platforms founded on clay, an important foundation failure mode arises from cumulative shear strain under cyclic loads. The major contribution to this cyclic strain accumulation comes from wave loads in sea states of high intensities. To analyze this and similar cumulative damage mechanisms, a probabilistic storm profile model is developed. Slepian random process models are used to estimate the temporal evolution of the significant wave height HS during a storm, during which HS exceeds a specified threshold. To predict storm profiles associated with any threshold, the model requires only conventional marginal wave statistics along with limited correlation information. Numerical results are shown for a North Sea location, where rare, high-threshold events can be verified by long hindcast histories. For an example foundation, predicted strain accumulation is compared with results from conventional storm profile models.
Effect of Forward Speed on the Roll Damping of Three Small Fishing Vessels
Authors: Haddara M. R. , Zhang S.
Published: June 2008

An extensive experimental program has been carried out to estimate roll damping parameters for three models of fishing vessels having different hull shapes and moving with forward speed. Roll damping parameters are determined using a novel method. This method combines the energy method and the modulating function method. The effect of forward speed, initial heel angle and the natural frequency on damping is discussed. A modification of Ikeda’s formula for lift damping prediction is suggested. The modified formula produces results which are in good agreement with the experiments.
Analysis of Non-Gaussian Surge Response of Tension Leg Platforms
Under Wind Loads
Authors: Kareem A. , Zhao J.
Published: June 2008

The nonlinearity in the wind loading expression for a complaint offshore structure, e.g., a tension leg platform (TLP), results in response statistics that deviate from the Gaussian distribution. This paper focuses on the statistical analysis of the response of these structures to random wind loads. The analysis presented here involves a nonlinear system with memory. As an improvement over the commonly used linearization approach, an equivalent statistical quadratization method is presented. The higher-order response cumulants are based on Volterra series. A direct integration scheme and Kac-Siegert technique is utilized to evaluate the response cumulants. Based on the first four cumulants, the response probability density function, crossing rates, and peak value distribution are derived. The results provide a good comparison with simulation. A nonlinear wind gust loading factor based on the derived extreme value distribution of nonlinear wind effects is formulated.
Strength of Tubular Members Containing Holes
Authors: Hsu T. M.
Published: June 2008

A small-scale, compressive-load test program was conducted at Chevron to determine the strength of tubular members with 1 to 3 holes. The parameters evaluated include the hole size, hole shape, hole location, and number of holes. Results from these tests provide a basis for platform ultimate strength calculations that are needed in making decisions on platform repairs. More than 50 specimens were tested in air under displacment control. Test specimen lengths were limited by the test apparatus to 45 in. (1,143 mm). Tubulars used in the test had an outside diameter of 3.5 in. (89 mm), which gave member slenderness ratios of about 40. The tests were needed because of the lack of relevant compression tests on members with holes. Based on test results, there appears to be a limiting value of hole size below which the compression-load capacity of the member is practically not affected by the existence of the hole. For example, a hole that is 10 percent of the member diameter does not significantly reduce member strength. This means remedial treatment is not necessary for many small holes, when ultimate strength is the controlling consideration. Nonlinear finite element shell analyses using both ADINA and FACTS computer programs and a simplified analysis using DENTA-II PC program were performed and results compared with data. We found that nonlinear finite element programs provide good predictions of capacities of members with holes, and that a simplified DENTA-II program provides adequate and efficient predictions.