bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication and Characterization of ZrB2‐Based Ceramic Using Synthesized ZrB2–LaB6 Powder
Authors: Spring Alex , Guo Wei‐Ming , Zhang Guo‐Jun , Wang Pei‐Ling , Krstic Vladimir D.
Published: June 2008

ZrB2–LaB6 powder was obtained by reactive synthesis using ZrO2, La2O3, B4C, and carbon powders. Then ZrB2–20 vol% SiC–10 vol% LaB6 (ZSL) ceramics were prepared from commercially available SiC and the synthesized ZrB2–LaB6 powder via hot pressing at 2000°C. The phase composition, microstructure, and mechanical properties were characterized. Results showed that both LaB6 and SiC were uniformly distributed in the ZrB2 matrix. The hardness and bending strength of ZSL were 17.06±0.52 GPa and 505.8±17.9 MPa, respectively. Fracture toughness was 5.7±0.39 MPa·m1/2, which is significantly higher than that reported for ZrB2–20 vol% SiC ceramics, due to enhanced crack deflection and crack bridging near SiC particles.
Body mass index and prevalence of obesity in a French cohort of patients with schizophrenia
Authors: Limosin F. , Gasquet I. , Leguay D. , Azorin J.‐M. , Rouillon F.
Published: June 2008

Objective:  To evaluate the distributions of body mass index in a large sample of patients with schizophrenia, and to examine the association between body weight and antipsychotic drugs.

Method:  The data source was baseline data from a national survey conducted in 2005–2006 in 5756 patients.

Results:  The mean age of the patients was 37.1 ± 11.8 years, and the mean BMI was 25.5 ± 5.2 kg/m2. In the final logistic regression model, the prevalence of obesity was significantly higher in female patients, age 40–59 vs. 18–29 years, patients in sheltered employment (vs. no income), out‐patients (vs. full‐time in‐patients) and patients treated with concomitant antidepressant. There was a higher rate of obesity, relative to an absence of antipsychotics at entry, for patients receiving the following individual drugs: clozapine, olanzapine, risperidone and amisulpride.

Conclusion:  In patients treated with atypical antipsychotics, we found a significantly higher prevalence of obesity than in those not treated with any antipsychotic medication.
Sequences of emotions in patients with borderline personality disorder
Authors: Reisch T. , Ebner‐Priemer U. W. , Tschacher W. , Bohus M. , Linehan M. M.
Published: June 2008

Objective:  To investigate sequences of emotions (temporal dependence of emotions) to identify specific patterns of borderline personality disorder (BPD).

Method:  The perceived emotions of 50 BPD patients and 50 healthy controls (HC) were monitored by using a hand‐held computer system for a 24‐h period in a daily life setting. Participants were prompted four times per hour to assess their current perceived emotions. Differences between BPD patients and HC in terms of activation, persistence and down‐regulation of emotions were analyzed.

Results:  Healthy controls in contrast to BPD patients more often activated joy and interest. BPD patients more often experienced persistence of anxiety and sadness. BPD patients more frequently switched from anxiety to sadness, from anxiety to anger and from sadness to anxiety. Anger was predominantly preceded by anxiety.

Conclusion:  Persistence of sadness and anxiety, as well as emotional oscillating between anxiety, sadness and anger are important aspects of the emotional dysregulation in BPD patients.
Influence of residual pockets on progression of periodontitis and tooth loss: Results after 11 years of maintenance
Authors: Matuliene Giedre , Pjetursson Bjarni E. , Salvi Giovanni E. , Schmidlin Kurt , Brägger Urs , Zwahlen Marcel , Lang Niklaus P.
Published: June 2008

Background: Limited evidence exists on the significance of residual probing pocket depth (PPD) as a predictive parameter for periodontal disease progression and tooth loss.

Aim: The aim of this study was to investigate the influence of residual PPD 5 mm and bleeding on probing (BOP) after active periodontal therapy (APT) on the progression of periodontitis and tooth loss.

Material and Methods: In this retrospective cohort, 172 patients were examined after APT and supportive periodontal therapy (SPT) for 3–27 years (mean 11.3 years). Analyses were conducted using information at site, tooth and patient levels. The association of risk factors with tooth loss and progression of periodontitis was investigated using multilevel logistic regression analysis.

Results: The number of residual PPD increased during SPT. Compared with PPD3 mm, PPD=5 mm represented a risk factor for tooth loss with odds ratios of 5.8 and 7.7, respectively, at site and tooth levels. The corresponding odds ratios for PPD=6 mm were 9.3 and 11.0 and for PPD7 mm 37.9 and 64.2, respectively. At patient level, heavy smoking, initial diagnosis, duration of SPT and PPD6 mm were risk factors for disease progression, while PPD6 mm and BOP30% represented a risk for tooth loss.

Conclusion: Residual PPD6 mm represent an incomplete periodontal treatment outcome and require further therapy.
Maternal tobacco smoking, nicotine replacement and neurobehavioural development
Authors: Pauly James R , Slotkin Theodore A
Published: June 2008

The adverse effects of prenatal cigarette smoke exposure on human reproductive outcomes are a major scientific and public health concern. In the United States, approximately 25% of women of childbearing age currently smoke cigarettes, and only a small percentage of these individuals quit after learning of their pregnancy. Women interested in smoking cessation during pregnancy have a number of options, including behavioural and pharmacological aids, but nicotine replacement therapy (NRT) is by far the most common approach. While NRT avoids exposure to the myriad compounds present in tobacco smoke, nicotine itself causes damage to the developing nervous system. The purpose of this article is to review the detrimental effects of developmental tobacco smoke exposure on short‐ and long‐term outcomes with particular emphasis on neurobehavioural consequences. In conclusion based on the clear, adverse effects of nicotine on brain development observed in human and animal studies, we suggest that safer alternatives for smoking cessation in pregnancy are badly needed.
Low birth weight and the developing vascular tree: a systematic review
Authors: Norman Mikael
Published: June 2008

Low birth weight (LBW) is a risk factor for hypertension, stroke and coronary heart disease in adults. Mechanisms underlying cardiovascular disease may therefore be initiated in early life. Studies to investigate the initiating events and emergence of vascular risk markers in infancy and childhood have been an area of particular interest in recent years. The aim of this review is to focus on the early development of the human vascular tree in relation to LBW. Specific characteristics, including endothelial function, intima–media thickness, microvascular density, arterial dimensions and elasticity, will be discussed. LBW due to different causes – poor foetal growth or preterm birth – results in different patterns of altered development of the vascular system, which can already be seen in infancy. Follow‐up studies in children and young adults indicate that vascular compromise in many ways persists in those born either small for gestational age or prematurely.

Conclusion: LBW is associated with structural and functional changes in the vascular tree, which have implications for cardiovascular health in adult life.
Romanticism/Secularization/Secularism
Authors: Jager Colin
Published: June 2008

The romantic period is often considered a time of secularization. However, recent critiques of the secularization thesis, as well as recent scholarly accounts of romanticism, have questioned this assumption. At the same time, a number of scholars have begun to analyze secularism itself. Secularism, some have suggested, actually ‘invents’ the concept of religion during the period of European colonialism. It is therefore not possible to investigate the question of ‘romanticism and religion’ as if ‘religion’ was a definite thing. However, the relationship between secularism and romanticism remains an important research topic. One question of particular interest is how literature came to be understood during the romantic period, and the degree to which literary reading is associated with secularism.
Demonstration of an anti‐oxidative stress mechanism of quetiapine
Authors: Xu Haiyun , Wang Haitao , Zhuang Lixia , Yan Bin , Yu Yingxin , Wei Zelan , Zhang Yanbo , Dyck Lillian E. , Richardson Steven J. , He Jue , Li Xiaokun , Kong Jiming , Li Xin‐Min
Published: June 2008

We have shown that quetiapine, a new antipsychotic drug, protects cultured cells against oxidative stress‐related cytotoxicities induced by amyloid β (Aβ)25‐35, and that quetiapine prevents memory impairment and decreases Aβ plaques in the brains of amyloid precursor protein (APP)/presenilin‐1 (PS‐1) double‐mutant mice. The aim of this study was to understand why quetiapine has these protective effects. Because the cytotoxicity of both Aβ(25‐35) and Aβ(1‐40) requires fibril formation, our first experiments determined the effect of quetiapine on Aβ(25‐35) aggregation. Quetiapine inhibited Aβ(25‐35) aggregation in cell‐free aqueous solutions and blocked the fibrillar aggregation of Aβ(25‐35), as observed under an electron microscope. We then investigated why quetiapine inhibits Aβ(25‐35) aggregation. During the aggregation of Aβ(25‐35), a hydroxyl radical (OH•) was released, which in turn amplified Aβ(25‐35) aggregation. Quetiapine blocked OH•‐induced Aβ(25‐35) aggregation and scavenged the OH• produced in the Fenton system and in the Aβ(25‐35) solution, as analyzed using electron paramagnetic resonance spectroscopy. Furthermore, new compounds formed by quetiapine and OH• were observed in MS analysis. Finally, we applied Aβ(25‐35) to PC12 cells to observe the effect of quetiapine on living cells. Aβ(25‐35) increased levels of intracellular reactive oxygen species and calcium in PC12 cells and caused cell death, but these toxic effects were prevented by quetiapine. These results demonstrate an anti‐oxidative stress mechanism of quetiapine, which contributes to its protective effects observed in our previous studies and explains the effectiveness of this drug for Alzheimer’s disease patients with psychiatric and behavioral complications.
Proteochemometric Modeling of the Inhibition Complexes of Matrix Metalloproteinases with N‐Hydroxy‐2‐[(Phenylsulfonyl)Amino]Acetamide Derivatives Using Topological Autocorrelation Interaction Matrix and Model Ensemble Averaging
Authors: Fernández Michael , Fernández Leyden , Caballero Julio , Abreu José Ignacio , Reyes Grethel
Published: June 2008

A target‐ligand QSAR approach using autocorrelation formalism was developed for modeling the inhibitory potency (pIC50) toward matrix metalloproteinases (MMP‐1, MMP‐2, MMP‐3, MMP‐9, and MMP‐13) of N‐hydroxy‐2‐[(phenylsulfonyl)amino]acetamide derivatives. Target and ligand structural information was encoded in the Topological Autocorrelation Interaction matrix calculated from 2D topological representation of inhibitors and protein sequences. The relevant Topological Autocorrelation Interaction descriptors were selected by genetic algorithm‐based multilinear regression analysis and Bayesian‐regularized genetic neural network approaches. A model ensemble strategy was employed for achieving robust and reliable linear and non‐linear predictors having nine topological autocorrelation interaction descriptors with square correlation coefficients of ensemble test‐set fitting (R2test) about 0.80 and 0.87, respectively. Electrostatic and hydrophobicity/hydrophilicity properties were the most relevant on the optimum models. In addition, the distribution of the inhibition complexes on a self‐organized map depicted target dependence rather than an inhibitor similarity pattern.
Return Performance Surrounding Reverse Stock Splits: Can Investors Profit?
Authors: Kim Seoyoung , Klein April , Rosenfeld James
Published: June 2008

We examine the long‐run return performance of over 1,600 firms with reverse stock splits. These stocks record statistically significant negative abnormal returns over the three‐year period following the month of the reverse split. The sample firms experience poor operating performances over the four years that include and follow the year of the reverse split, which suggests informational inefficiencies. Because these stocks have unique financial characteristics, we also show that they would be very difficult to sell short. Thus, arbitrageurs would be restricted in their ability to earn abnormal profits, even if they correctly anticipated a price decline.
Stock Splits in Switzerland: To Signal or Not to Signal?
Authors: Kunz Roger M. , Rosa‐Majhensek Sandro
Published: June 2008

In Switzerland, the existence of a mandatory minimum par value inhibited many companies from splitting their stocks as they already traded at their minimum par value. These Swiss companies could split their stocks only after the legal minimum par value was lowered in July 1992 and again in May 2001. These two events provide rare opportunities to distinguish between stock splits that signal a permanent increase in stock price and splits that are merely a reaction to a regulatory change and thus have other motives. The significant return differences between the two samples are in line with the hypothesis that splits are a means to send positive signals to the stock market. Furthermore, while trading volumes remained largely unaffected after stock splits, relative tick sizes generally increased after a stock split, and bid‐ask spreads often increased after a stock split.
The Wealth Effect of Japanese‐US Strategic Alliances
Authors: Chang Shao‐Chi , Chen Sheng‐Syan , Lai Jung‐Ho
Published: June 2008

We investigate the wealth impact for Japanese and US firms that announce nonequity strategic alliances. We find that on average, both Japanese and US shareholders benefit from the formation of international alliances. We also find that shareholders earn larger abnormal returns in these alliances when the partnering firms are relatively small in size, have higher growth opportunities, or are less profitable. We show that both Japanese and US partnering firms display significant improvements in operating performance over the three‐year period subsequent to the formation of international alliances.
Quiet, Nonconsumptive Recreation Reduces Protected Area Effectiveness
Authors: Reed Sarah E. , Merenlender Adina M.
Published: June 2008

Protected areas around the world were created with the goals of preserving biodiversity and providing nature‐based recreation opportunities for millions of people. This dual mandate guides the management of the majority of the world's protected areas, but there is growing evidence that quiet, nonconsumptive recreation may not be compatible with biodiversity protection. We combined noninvasive survey techniques and DNA verification of species identifications to survey for mammalian carnivores in 28 parks and preserves in northern California. Paired comparisons of neighboring protected areas with and without recreation revealed that the presence of dispersed, nonmotorized recreation led to a five‐fold decline in the density of native carnivores and a substantial shift in community composition from native to nonnative species. Demand for recreation and nature‐based tourism is forecasted to grow dramatically around the world, and our findings suggest a pressing need for new approaches to the designation and management of protected areas.
Duffing Oscillator With Parametric Excitation: Analytical and Experimental Investigation on a Belt-Pulley System
Authors: Michon Guilhem , Manin Lionel , Parker Robert G. , Dufour Régis
Published: June 2008

This paper is devoted to the theoretical and experimental investigation of a sample automotive belt-pulley system subjected to tension fluctuations. The equation of motion for transverse vibrations leads to a Duffing oscillator parametrically excited. The analysis is performed via the multiple scales approach for predicting the nonlinear response, considering longitudinal viscous damping. An experimental setup gives rise to nonlinear parametric instabilities and also exhibits more complex phenomena. The experimental investigation validates the assumptions made and the proposed model.
Motion Planning and Control of a Tractor With a Steerable Trailer Using Differential Flatness
Authors: Ryu Ji-Chul , Agrawal Sunil K. , Franch Jaume
Published: June 2008

This paper presents a methodology for trajectory planning and tracking control of a tractor with a steerable trailer based on the system’s dynamic model. The theory of differential flatness is used as the basic approach in these developments. Flat outputs are found that linearize the system’s dynamic model using dynamic feedback linearization, a subclass of differential flatness. It is demonstrated that this property considerably simplifies motion planning and the development of controller. Simulation results are presented in the paper, which show that the developed controller has the desirable performance with exponential stability.
Calculation of Fluid Flow Distribution Inside a Compact Ceramic High Temperature Heat Exchanger and Chemical Decomposer
Authors: Ponyavin Valery , Chen Yitung , Cutts James , Wilson Merrill , Hechanova Anthony E.
Published: June 2008

Numerical analysis of flow distribution inside a compact ceramic high temperature heat exchanger and chemical decomposer (thereafter, heat exchanger), which will be used for hydrogen production, wherein the sulfur iodine thermochemical cycle is performed. To validate the numerical model, experimental investigation of the heat exchanger is accomplished. The study of the flow distribution in the base line design heat exchanger shows that the design has large-flow maldistribution and the reverse flow may occur at poor inlet and outlet manifold configurations. To enhance uniformity of the flow rate distribution among the heat exchanger internal channels, several improved designs of the heat exchanger manifolds and supply channels are proposed. The proposed designs have a sufficiently uniform flow rate distribution among the internal channels, with an appropriate pressure drop.
Identification of Flow Structures on a LP Turbine Blade Due to
Periodic Passing Wakes
Authors: Sarkar S.
Published: June 2008

The paper describes the flow structures on the suction surface of a highly cambered low-pressure turbine (LPT) blade (T106 profile) subjected to periodic convective wakes. A separation bubble on the rear half of the suction side of the blade was found to form under the operating condition due to the highly diffusive boundary layer. Interactions of migrating wakes with this separated boundary layer trigger rollup of the shear layer leading to transition and the appearance of coherent vortices. To characterize the dynamics of these large-scale structures, a proper orthogonal decomposition is pursued on both the fluctuating velocity and the vorticity fields generated by large-eddy simulations (LESs) of wake passing over the LPT blade for a Reynolds number Re=1.6×105. The first two modes clearly depict the rollup of the unstable shear layer and formation of large-scale vortex loops that contain a major fraction of the fluctuation energy. The present LES, at least in a qualitative sense, illustrates the large-scale motions in the outer layer and dynamics of vortical structures in a separated boundary layer excited by external perturbations.
Numerical Simulation of 3D Cavitating Flows: Analysis of Cavitation Head Drop in Turbomachinery
Authors: Pouffary Benoît , Patella Regiane Fortes , Reboud Jean-Luc , Lambert Pierre-Alain
Published: June 2008

The numerical simulation of cavitating flows in turbomachinery is studied at the Turbomachinery and Cavitation team of Laboratoire des Ecoulements Géophysiques et Industriels (LEGI), Grenoble, France in collaboration with the French space agency (Centre National d’Etudes Spatiales, CNES), the rocket engine division of Snecma and Numeca International. A barotropic state law is proposed to model the cavitation phenomenon and this model has been integrated in the CFD code FINE/TURBO™. An analysis methodology allowing the numerical simulation of the head drop induced by the development of cavitation in cold water was proposed and applied in the case of two four-bladed inducers and one centrifugal pump. Global results were compared to available experimental results. Internal flows in turbomachinery were investigated in depth. Numerical simulations enabled the characterization of the mechanisms leading to the head drop and the visualization of the effects of the development of cavitation on internal flows.
Passive Control Around the Two-Dimensional Square Back Ahmed Body Using Porous Devices
Authors: Bruneau Charles-Henri , Mortazavi Iraj , Gilliéron Patrick
Published: June 2008

The control of two-dimensional flows around the square back Ahmed body is achieved by using porous devices added on some parts of the body. The square back Ahmed body is considered either in an open domain or on top of a road. The modeling of the flow in different media is performed by means of the penalization method. A good choice of the location of the porous interfaces yields a significant improvement of the aerodynamic quantities, especially for the square back body.
Passive Control of Transonic Cavity Flow
Authors: MacManus David G. , Doran Diane S.
Published: June 2008

Open cavities at transonic speeds can result in acoustic resonant flow behavior with fluctuating pressure levels of sufficient intensity to cause significant damage to internal stores and surrounding structures. Extensive research in this field has produced numerous cavity flow control techniques, the more effective of which may require costly feedback control systems or entail other drawbacks such as drag penalties or rapid performance degradation at off-design condition. The current study focuses on the use of simple geometric modifications of a rectangular planform cavity with the aim of attenuating the aeroacoustic signature. Experiments were performed in an intermittent suck-down transonic wind tunnel by using a typical open flow rectangular planform cavity, which was modularly designed such that the leading and trailing edge geometries could be modified by using a family of inserts. The current work focused on a variety of recessed leading edge step arrangements. Configurations were tested at transonic Mach numbers spanning the range Mach 0.7–0.9, and unsteady pressure measurements were recorded at various stations within the cavity in order to obtain acoustic spectra. The most effective configuration at Mach 0.9 was the leading edge step employing a step height to step length ratio of 0.4. This configuration achieved a tonal attenuation of up to 18.6dB and an overall sound pressure level (OASPL) reduction of approximately 7.5dB. This is a significant level of noise suppression in comparison with other passive control methods. In addition, it offers the additional benefits of being a simple geometric feature, which does not rely on placing flow effectors into the high-speed grazing flow.
The Validity of Standard Test Methods for Characterizing Weld Fracture
Authors: Graham S. M. , Reuter W. G. , Lloyd W. R. , Epstein J. S.
Published: June 2008

Standard methods for testing fracture toughness of homogeneous materials are currently being applied to welds. A weld is, by nature, a heterogeneous structure containing zones with different microstructures and mechanical properties. The validity of using fracture parameters developed for homogeneous materials to characterize fracture of welds has not been established. Tests were conducted to investigate whether the extension of a crack along an interface is governed by the same fracture parameters used to predict fracture in homogeneous materials. The tests involved measuring the displacement fields around a crack tip in the interface between two materials with matched elastic properties and differing yield strengths. The form of the displacement distribution was then compared with the theoretical displacements for linear elasticity and nonlinear elasticity with power-law hardening.
Separation Points on a Cylinder in Oscillating Flow
Authors: Sarpkaya T. , Butterworth W.
Published: June 2008

Experiments were performed in a U-shaped oscillating-flow tunnel, with fixed smooth and rough circular cylinders, to determine the circumferential as well as spanwise excursion of the separation points for representative values of the governing parameters. Differential-pressure probes (sublayer fences), flush-mount hot film sensors, and flow visualization were used to determine the instantaneous positions of the separation points. Subsequently, small smooth cylinders, oscillating in water otherwise at rest, and two types of flow visualization were used to obtain additional data. The results have shown that the separation points undergo large angular excursions during a given cycle, the degree of excursion depending primarily on the Reynolds number, Keulegan-Carpenter number, and the relative roughness. The separation data obtained in this investigation are expected to form the basis of related numerical studies in providing guidance for their formulation as well as comparison for their accuracy and validity.
On the Response of Elastic-Plastic Tubes Under Combined Bending and Tension
Authors: Dyau J. Y. , Kyriakides S.
Published: June 2008

This paper is concerned with the response of long, relatively thin-walled tubes bent into the plastic range in the presence of axial tension. The work is motivated by the design needs of pipelines installed and operated in deep offshore waters. The problem is studied through a combination of experiment and analysis. In the experiments, long metal tubes were bent over a smooth, circular, rigid surface (mandrel). Bending of the tubes was achieved by shear and axial end loads. The experimental arrangement is such that a significant section of the test specimen is loaded and deformed in an axially uniform fashion. The ovalization induced in the specimen was measured as a function of the axial load in the tube for two mandrel radii. A two-dimensional numerical simulation of the problem has been developed and validated against the experimental results. This analysis was used to conduct a parametric study of the effect of tension on the ovalization induced in a long tube during bending.
Parallel System Approach for Vector Out-Crossing
Authors: Hagen O̸. , Tvedt L.
Published: June 2008

The mean crossing rate of a stochastic process out-crossing a safe domain is calculated using methods from time-independent reliability theory. The method is developed from Madsen’s formula which expresses the mean up-crossing rate of a scalar process through a specified level as a parallel system sensitivity measure. The method is applicable to stationary as well as nonstationary stochastic vector processes provided the random variables describing the process and the time-derivative process at time t can be mapped jointly into a set of independent standardized random normal variables. This is identical to the restriction imposed on the random variables using the first and second-order reliability methods (FORM, SORM), and is not very restrictive. Thus, quite general stochastic models can be treated. Also, closed-form results have been developed. In this paper the mean crossing rate for the stationary Gaussian process crossing into a polyhedral convex set is given. The method is demonstrated to give good results by examples.
Uncertainty of Design Parameters From Viewpoint of Extreme Statistics
Authors: Goda Y.
Published: June 2008

Statistical variability of a sample of extreme data has been examined by means of Monte Carlo simulations. The Fisher-Tippett types I and II, the Weibull, and the log-normal distributions were chosen for the examination. The sample size covered from 10 to 400, and 10,000 runs were carried out for each combination of sample size, censoring rate, and distribution function. Empirical formulas and tables are presented for the mean and the coefficient of variation of the standard deviation of a sample, the standard deviation of return value, and the confidence interval of return period.
A Submerged Compliant Breakwater
Authors: Williams A. N. , Geiger P. T. , McDougal W. G.
Published: June 2008

A numerical technique is utilized to investigate the dynamics of a submerged compliant breakwater consisting of a flexible, beamlike structure anchored to the seabed and kept under tension by a small buoyancy chamber at the tip. The fluid motion is idealized as linearized, two-dimensional potential flow and the equation of motion of the breakwater is taken to be that of a one-dimensional beam of uniform flexural rigidity and mass per unit length subjected to a constant axial force. The boundary integral equation method is applied to the fluid domain, modifications are made to the basic formulation to account for the zero thickness of the idealized structure and the singularity in the fluid velocity which occurs at the breakwater tip. The dynamic behavior of the breakwater is described through an appropriate Green function. Numerical results are presented which illustrate the global influence of the tip singularity on the solution and the effects of the various wave and structural parameters on the efficiency of the breakwater as a barrier to wave action. Small-scale physical model tests were also carried out to validate the foregoing theory. In general, the agreement between experimental and numerical results was reasonable, but with considerable scatter.
Three-Dimensional Nonlinear Dynamic Analysis Method of Underwater Line Structure and Its Validation
Authors: Suzuki H. , Yoshida K.
Published: June 2008

A 3-dimensional nonlinear method for analysis of underwater line structures is presented. This analysis method is formulated by the finite element method, and dynamic behavior of the structures is solved in time domain. The motion equations are solved by Newmark time integration scheme. The method can handle all nonlinearities relating to the dynamic motion of the line structures such as hydrodynamic nonlinearity, geometrical nonlinearity, nonlinear boundary condition, and so on. The Newton method is employed to improve stability of the iteration solution when a dynamic equilibrium condition is obtained. The computational method has been verified through comparison with model tests conducted by the authors. These tests required the development of a general-purpose ultrasonic ranging system, which is described briefly. Usually high accuracy is required for the ranging system because of the small size of models used in the basin test, and high frequency is employed. By this system, coordinates of maximum 16 points can be determined at an accuracy of 1 mm.
Economic Risk Analysis of Offshore Projects
Authors: Bitner-Gregersen E. M. , Lereim J. , Monnier I. , Skjong R.
Published: June 2008

A quantitative analysis of economic risk associated with large investments in offshore oil and gas field development and production is presented. The analysis is intended as a supporting tool in decision-making faced with uncertainty and risk, to study the effect of alternative decisions in an easy manner. The descriptors for the project assessment, such as the Internal Rate of Return (IRR) and Net Present Value (NPV) are applied. The study demonstrates first the impacts of early pilot production (EPP) prior to a main oil field development on the field economy of an oil field development and production installation. Furthermore, the result of cases which reflect relevant situations connected with cost overruns are presented, as well as derivation of rational decision criteria for termination/continuation of a project subjected to cost overruns. Finally, an oil field development project scheduling is demonstrated.
Wave Diffraction Theory—Some Developments in Linear and Nonlinear Theory
Authors: Eatock Taylor R. , Chau F. P.
Published: June 2008

The paper discusses recent developments aimed at improving the efficiency by which converged first and second-order results may be obtained. A higher-order element discretization of a novel integral equation is described. It is shown that this is capable of providing highly accurate first-order results based on a relatively small number of elements. Results are also given for the nonlinear diffraction problem, including comparisons with an analytical solution for a vertical cylinder. Practical use of these developments is illustrated by results for the second-order free surface profile in the vicinity of a tension leg platform.
Structural Engineering Aspects of the STAR Platform
Authors: Waegter J. , Olsen K. B. , Sorensen K. A.
Published: June 2008

Based on the economic frames of the late eighties, the general urge to develop cheap and small platforms for marginal fields is outlined. Through a case story covering main aspects of the structural development and design of the STAR platforms, originated by Mærsk Olie og Gas AS, it is demonstrated how a new, cheap jackup installed platform type has been developed for shallow Danish North Sea conditions. Due to the platform’s relatively slender layout, it is more susceptible to dynamic loads than traditional jackets. Therefore, special investigations have been carried out for ship impact, fatigue, vortex shedding and pile driving-induced vibrations. Both the approach chosen for the analyses and design, as well as typical results, have been included. Finally, the present record of this new platform has been given.
Spectral Modeling of Sea States With Multiple Wave Systems
Authors: Guedes Soares C. , Nolasco M. C.
Published: June 2008

The spectral models of individual wave systems have one peak and are described by theoretical models that have gained general acceptance. This work deals with sea states with more than one wave system, leading to spectral models with two or more peaks. Use is made of spectra derived from measurements off the Portuguese Coast and data is provided as to their probability of occurrence as well as about the dependence of the spectral parameters on the significant wave height and peak period. It is shown that wind-dominated and swell-dominated two-peaked spectra tend to occur in different areas of the scatter diagram. The spectral parameters of the two-peaked spectra show little correlation with significant wave height and peak period.
Redundancy Measures for Design and Evaluation of Structural Systems
Authors: Frangopol D. M. , Iizuka M. , Yoshida K.
Published: June 2008

Despite the fact that the need for structural redundancy has already been recognized by several standard specifications, no criteria to quantify redundancy in design and evaluation of structural systems are explicitly given within these specifications. The purpose of this paper is to discuss both deterministic and probabilistic measures for design and evaluation of structural systems. A comparison of some of the proposed redundancy measures is presented via numerical examples and observations pertaining to the ranges of their applicability are made.
Experimental Study of Ship Internal Waves—The Supersonic Case
Authors: Ma H. , Tulin M. P.
Published: June 2008

Internal waves produced by a ship traveling faster than the fastest internal waves (supersonic case) were investigated experimentally in our laboratory in a wide tank using averaging conductivity wave gages developed for this investigation. The wave gage is similar to the conductivity probe, but has space-averaging electrodes. An array of seven such gages was used in a wave tank with dimensions 12 ft length, 8 ft width, 2 ft depth. The water in the tank was stratified with salt to obtain desired density distributions. A spheroid, split vertically, was towed against and along a sidewall to simulate a moving ship. Simultaneous wave profiles at various distances normal to the track of the ship were obtained for different Froude numbers and density distributions. The internal wave patterns were calculated from the measured data and compared with theoretical results. The amplitude on the first crest of the internal wave field is also plotted against the distance from the ship, and a limited comparison with theory is made. The experimental method developed for this study is sensitive, simple and reliable. It may serve to obtain a data base for ship-generated internal waves under a variety of conditions.
Frequency Domain Analysis of In-Line Forces on Circular Cylinders in Random Oscillatory Flow
Authors: Longoria R. G. , Miksad R. W. , Beaman J. J.
Published: June 2008

Experiments were conducted to study random hydrodynamic loading of smooth, rigidly mounted circular cylinders exposed to random oscillatory flow conditions. The experiments were conducted in a water tunnel for statistical Keulegan-Carpenter numbers ranging from KCr = 6.8 to 11.6 and statistical Reynold’s numbers from Rer = 8211 to 20169 under broad and narrow-band flow conditions. A two-input/single-output frequency domain model for the in-line force is used to directly identify frequency-dependent inertia and drag coefficients. This model was also used to show the relative strength of the inertia and drag components in the frequency domain for different random flow conditions parameterized by KCr, Rer and the velocity spectral width, q. This analysis illustrates the effect of statistical flow parameters (KCr, Rer and q) on the nonlinear behavior of the in-line forces. Estimates of the in-line force power spectral density under random flow conditions are determined using the two-input/single-output model and compared to the method for estimating wave forces on a cylindrical structure by Borgman (1967, 1972).
Offshore Hydrodynamics
Authors: Sarpkaya T.
Published: June 2008

In this paper, we present several applied as well as fundamental research problems related to the future needs of the offshore engineering. The paper starts out with a detailed discussion of the current uncertainties and constraints. Then, specific research issues on environmental input conditions, on the role of computational fluid dynamics, and on damping and dynamic response are presented. It is suggested that an appreciation of the input parameters, acquisition of extensive data to properly characterize the ocean environment, development of new methods and tools to acquire relevant data, extensive use of the computational methods, basic/applied research on the dynamic response and damping of structures, use of new materials, science-and-technology transfer from sister disciplines (e.g., aerospace industry, keeping in mind the complexities brought about by the presence of the air-water interface), and other related research will significantly enhance our ability to design and build a variety of safer and economical offshore structures in deeper waters as well as over marginal fields in the next few decades. This herculean effort will require several decades of complementary experimental, numerical and analytical studies of ocean-structure interaction which will serve to elucidate the basic as well as applied fluid mechanics phenomena relevant to the offshore mechanics.
Evaluation of FCAW Consumables for Offshore and Arctic Structure Fabrication
Authors: Bala S. R. , Malik L. , Braid J. E. M.
Published: June 2008

A primary consideration in the welding of structures for service in Canadian offshore and arctic regions is the toughness of weld metals required at very low ambient temperatures (−30°C to −60°C). To assess the suitability of cored wires for applications in these environments, some currently available commercial consumables for the flux-cored arc welding (FCAW) process were evaluated. Cored wires belonging to four different categories: basic, rutile, metal-cored and innershield, were used to prepare welds with similar welding procedures. Weld metal Charpy V-notch (CVN) and crack tip opening displacement (CTOD) tests were carried out and the effect of weld metal composition, microstructure and inclusion content in the weld metal toughness was examined. The Charpy transition temperatures and the CTOD toughness results indicated that, of the 16 wires tested, there were only seven that would be suitable for critical applications.
Probabilistic Analysis of Local Ice Pressures
Authors: Jordaan I. J. , Maes M. A. , Brown P. W. , Hermans I. P.
Published: June 2008

Extensive work in recent years has been carried out on the calculation of global ice loads on a probabilistic basis. An analysis method is presented for local ice pressures, which yields values of pressure for specific values of exceedance probability. In developing this method, particular attention has been paid to problems of exposure (length, position and number of impacts), as well as the area of exposure (area within area versus nominal contact area). The solution has been formulated for a series of discrete impacts, e.g., rams by a vessel, or a series of periods of continuous interactions. Data for the MV CANMAR Kigoriak and USCGC Polar Sea were ranked and curves were fitted through the tail of probability plots for three panel sizes. This allowed determination of exceedance probabilities of the design coefficients for pressure as a function of area. The method developed was then applied to an example for a ship based on the data and expected number of rams per year. Formulas useful in the design of structures in ice are presented.
Distribution of Crest Amplitudes in Severe Seas With Breaking
Authors: Kriebel D. L. , Dawson T. H.
Published: June 2008

A theoretical model is presented for the probability distribution of wave crest amplitudes in severe seas states with wave breaking. As the severity of a sea state increases, nonlinearities cause an increase in the amplitudes of the largest wave crests with a subsequent modification of the distribution of wave crest amplitudes from the linear Rayleigh theory. In this paper, a theory for the probabilities of these nonlinear crest amplitudes is first reviewed based on earlier work. The further limitations on these nonlinear crest amplitudes by wave breaking are then considered. As a result, a theoretical model is presented to account for both: 1) the nonlinear increase in the highest wave crests, and 2) the selective reduction of some fraction of these high crests due to wave breaking. This model is then verified using several sets of laboratory data for severe breaking seas having approximate JONSWAP wave spectra.
Dead-Water Effects of a Ship Moving in Stratified Seas
Authors: Miloh T. , Tulin M. P. , Zilman G.
Published: June 2008

A linearized theory is presented for the dead-water phenomena. A two-layer fluid model of finite depth is assumed and the solutions for both the wave resistance, as well as the interface and free-surface disturbances, are obtained in terms of Green’s function. Numerical solutions are given for the case of a semi-submersible slender-body (prolate spheroid) moving steadily on the free-surface.
Fatigue Life Prediction of Welded Joints for Offshore Structures Under Variable Amplitude Loading
Authors: Bell R. , Vosikovsky O.
Published: June 2008

This paper describes the development of a fracture mechanics model for the prediction of fatigue life of welded joints subjected to variable amplitude loading. The prediction program is based on the integration of the Paris equation. A novel feature of this program are relationships which account for the development, growth and coalescence of multiple cracks that occur at the weld toe. These relationships or forcing functions were developed from extensive monitoring of the initiation and crack shape development of multiple cracks during experimental tests. Data is also presented on a series of variable amplitude tests performed on welded T-plate joints loaded in 3-point bending using the common load sequence (COLOS) at a stress ratio of R=−1. These results are presented in terms of effective and root mean square stress ranges. The experimental data are used to validate the life prediction results from the growth model. A discussion is also included on the proportion of the compressive stress range to be included as an effective stress range in the prediction model calculations.
A Comparison of the Near-Threshold Corrosion Fatigue Crack Propagation Rates in Mil S-24645 HSLA Steel and Its Weld Metal
Authors: Todd J. A. , Chen L. , Yankov E. Y. , Tao H.
Published: June 2008

Near-threshold corrosion fatigue crack propagation studies have been conducted using compact tension specimens of Mil S-24645 HSLA steel and a compatible weld metal in air, ASTM seawater at the free corrosion potential, and ASTM seawater with −0.8V and −1.0V (SCE) cathodic protection. Tests were conducted at 10 Hz and a stress ratio, R = 0.1. The weld metal exhibited slower crack growth rates and higher threshold stress intensity ranges in both air and ASTM seawater than the base metal. However, the weld metal itself exhibited similar behavior in air, ASTM seawater and under cathodic protection, giving a threshold stress intensity range of 10 to 12.7 ksi in1/2 (11 to 14 MPa m1/2). With the exception of the weld metal tested in air, after correction for crack closure, the effective threshold stress intensity range was reduced to the range 3.2 to 5.0 ksi in1/2 (3.5 to 5.5 MPa m1/2). Metal wedges, approximately 5 to 10 μm (1–2 grain sizes), which developed during the tests, were observed to contribute to crack closure in the −1.0V (SCE) cathodically protected specimens.
Forces and Moments on a Small Body Moving in a 3-D Unsteady Flow (With Applications to Slender Structures)
Authors: Foulhoux L. , Bernitsas M. M.
Published: June 2008

Complete expressions are derived for the inertia forces and moments acting on a small body in a six-degree-of-freedom motion in a three-dimensional unsteady flow in an unbounded ideal fluid. The far-field approximation of the body motion is represented by a series of multipoles located at the origin of the body. Unsteady terms are expanded in a dual series to the multipole series. Lagally integrals are expressed in terms of multipoles as well, by using Legendre polynomial expansions. New inertia force expressions are derived by truncating the multipole series after the quadrupoles. Corresponding terms for moments are also developed. The derived formulas are still compact enough for engineering applications. Many practical problems involving fixed and oscillating cylinders, piles, and risers are studied numerically. Comparisons to the Morison equation formulation prove that the nonlinear convective terms are not negligible in multidimensional relative flows.
Near-Threshold Fatigue Crack Growth Behavior of Mil S-24645 HSLA Steel and Its Weldments
Authors: Todd J. A. , Chen L. , Yankov E. Y.
Published: June 2008

The near-threshold corrosion fatigue crack propagation behavior of Mil S-24645 HSLA steel, its weld metal and heat-affected zone have been studied in simulated marine environments. Tests were conducted in air and ASTM seawater, at both the free corrosion potential and −1.0V (SCE), using a frequency of 0.2 Hz and a stress ratio, R = 0.1. The results were compared with previous data for Mil S-24645 and ASTM A710 steel tested at frequencies of 10 and 2 Hz. The influence of frequency, microstructure, and cathodic protection on crack closure contributions in the near-threshold regime will be discussed.
Nonlinear Dynamic Response of a Simple Ice-Structure Interaction
Model
Authors: Karr D. G. , Troesch A. W. , Wingate W. C.
Published: June 2008

The problem addressed is the continuous indentation of a ship or offshore structure into an ice sheet. The impacting ship or offshore structure is represented by a mass-spring-dashpot system having a constant velocity relative to the ice sheet. The dynamic response of this simple analogue model of ice-structure interaction is studied in considerable detail. The complicated, highly nonlinear dynamic response is due to intermittent ice breakage and intermittent contact of the structure with the ice. Periodic motions are found and the periodicity for a particular system is dependent upon initial conditions. For a representative system, a Poincare´ map is presented showing the fixed points. A description of some of the effects of random variations in system parameters is also presented. Some implications of these findings regarding structural design for ice interaction are discussed.