bluuebunny/crossref_metadata_2025 huggingface dataset:
A qualitative assessment of non‐carious cervical lesions in extracted human teeth
Authors: Nguyen C , Ranjitkar S , Kaidonis JA , Townsend GC
Published: February 2008

Background:  Opinions vary about the causes of non‐carious cervical lesions (NCCLs). They have been attributed to toothbrush abrasion, acid corrosion (commonly termed dental erosion), and abfraction. The purpose of this study was to examine the microwear details of NCCLs in a collection of extracted human teeth using scanning election microscopy (SEM).

Methods:  Negative replicas of large NCCLs in 24 extracted human teeth were obtained in polyvinylsiloxane impression material (Light Body Imprint ™II, 3M ESPE) and viewed under SEM.

Results:  All NCCLs extended from the cemento‐enamel junction to the root surface and they displayed a variety of wedge‐shaped appearances. There was evidence of both abrasion and corrosion in 18 of the 24 teeth (75.0 per cent), abrasion only in one tooth (4.2 per cent) and corrosion only in five teeth (20.8 per cent). Horizontal furrows with smooth edges and minor scratch marks, characteristic of abrasion and corrosion, were noted in 13 teeth (54.2 per cent).

Conclusions:  Based on microscopic assessment of a sample of extracted teeth, it appears that abrasion and corrosion are common associated aetiological factors in the formation of NCCLs.
Working practices and job satisfaction of Victorian dental hygienists
Authors: Hopcraft M , McNally C , Ng C , Pek L , Pham TA , Phoon WL , Poursoltan P , Yu W
Published: February 2008

Background:  Increasing demand for dental services and a projected shortage in the oral health workforce in Victoria has focused attention on dental hygienists as one mechanism for increasing the supply of dental services. Understanding the dental hygienist workforce is essential in order to plan effectively for the future delivery of dental services in Victoria.

Methods:  A postal survey of a random sample of Victorian dental hygienists was undertaken in 2006. Data on hygienists’ demographic characteristics, current dental practice, history of career breaks, aspects of clinical practice and job satisfaction were collected.

Results:  A response rate of 77 per cent was achieved. A total of 94.0 per cent of hygienists were currently working as a dental hygienist, working an average of 28.7 hours per week. Younger hygienists worked longer hours than their older colleagues. Career breaks were common, with 44.8 per cent reporting a career break of greater than one month, predominantly for child rearing, with a mean career break of 20.1 months. Hygienists reported a high level of satisfaction with most aspects of their employment.

Conclusions:  Victorian hygienists worked predominantly in private practices in metropolitan Melbourne, providing a range of preventive and periodontal services. Understanding the working patterns of dental hygienists is critical as hygienist numbers expand in the future, in order to undertake thorough evidence‐based workforce planning.
Cross‐pinning: the philosophy of retrievability applied practically to fixed, implant‐supported prostheses
Authors: Gervais MJ , Hatzipanagiotis P , Wilson PR
Published: February 2008

Biologic and technical complications are widely reported in the dental literature and often compromise the functional and/or aesthetic features of fixed, implant‐supported prostheses. Managing complications without damaging or destroying a restoration is an obvious advantage of implant‐based dentistry where the option of prosthetic retrievability is almost always available. The technique of cross‐pinning uses a transverse screw to secure a prosthesis to a milled implant abutment, allowing prosthetic retrievability irrespective of dental implant alignment. This study presents guidelines for cross‐pinning implant‐supported prostheses based on resistance form, screw mechanics and natural tooth contours. The technical aspects of cross‐pinning are also discussed using examples from four implant systems.
Social Psychology, Moral Character, and Moral Fallibility*
Authors: BESSER‐JONES LORRAINE
Published: February 2008

In recent years, there has been considerable debate in the literature concerning the existence of moral character. One lesson we should take away from these debates is that the concept of character, and the role it plays in guiding our actions, is far more complex than most of us initially took it to be. Just as Gilbert Harman, for example, makes a serious mistake in insisting, plain and simply, that there is no such thing as character, defenders of character also make a mistake to the extent that they imply there is no problem raised by the psychological literature for either the concept of character or the nature of character‐based ethics. My hope for this paper is to avoid both of these mistakes by first, exploring exactly what is the concept of character that is so firmly rooted in our philosophical and everyday thinking; and second, exploring the implications of the psychological literature for this appropriately understood concept of character. In so doing, I will come to a resolution that vindicates the existence of character, while at the same time calls attention to the real and serious problem suggested by the psychological evidence. This, we will see, is a problem of moral motivation.
Assertion, Practical Reason, and Pragmatic Theories of Knowledge
Authors: LEVIN JANET
Published: February 2008

Defenders of pragmatic theories of knowledge (such as contextualism and sensitive invariantism) argue that these theories, unlike those that invoke a single standard for knowledge, comport with the intuitively compelling thesis that knowledge is the norm of assertion and practical reason. In this paper, I dispute this thesis, and argue that, therefore, the prospects for both “high standard” and “low standard” invariantist theories are better than the pragmatists contend. I also provide a limited defense of the “high standard” approach, and contend that if one abandons the thesis that knowledge is the norm of assertion and practical reason, the most serious arguments against it lose their force.
Three-Dimensional Repeated Elasto-Plastic Point Contacts, Rolling, and Sliding
Authors: Chen W. Wayne , Wang Q. Jane , Wang Fan , Keer Leon M. , Cao Jian
Published: February 2008

Accumulative plastic deformation due to repeated loading is crucial to the lives of many mechanical components, such as gears, stamping dies, and rails in rail-wheel contacts. This paper presents a three-dimensional numerical model for simulating the repeated rolling or sliding contact of a rigid sphere over an elasto-plastic half-space. This model is a semi-analytical model based on the discrete convolution and fast Fourier transform algorithm. The half-space behaves either elastic-perfectly plastically or kinematic plastically. The analyses using this model result in histories of stress, strain, residual displacement, and plastic strain volume integral (PV) in the half-space. The model is examined through comparisons of the current results with those from the finite element method for a simple indentation test. The results of rolling contact obtained from four different hardening laws are presented when the load exceeds the theoretical shakedown limit. Shakedown and ratchetting behaviors are discussed in terms of the PV variation. The effect of friction coefficient on material responses to repeated sliding contacts is also investigated.
Robust Design Optimization in Computational Mechanics
Authors: Capiez-Lernout E. , Soize C.
Published: February 2008

The motivation of this paper is to propose a methodology for analyzing the robust design optimization problem of complex dynamical systems excited by deterministic loads but taking into account model uncertainties and data uncertainties with an adapted nonparametric probabilistic approach, whereas only data uncertainties are generally considered in the literature by using a parametric probabilistic approach. The possible designs are represented by a numerical finite element model whose design parameters are deterministic and belong to an admissible set. The optimization problem is formulated for the stochastic system as the minimization of a cost function associated with the random response of the stochastic system including the variability of the stochastic system induced by uncertainties and the bias corresponding to the distance of the mean random response to a given target. The gradient and the Hessian of the cost function with respect to the design parameters are explicitly calculated. The complete theory and a numerical application are presented.
A Strain Gradient Model for Fracture Prediction in Brittle Materials
Authors: Li Jia
Published: February 2008

In this paper, we present a new model to predict the fracture in brittle materials from a geometrical weakness presenting an arbitrary stress concentration. The main idea is to combine the strain gradient elasticity with a cohesive model that includes both the displacement and the rotation jumps between the cohesive surfaces in the separation law. Three material parameters were used in the establishment of the fracture criterion. The first two parameters are the commonly used σc, the ultimate stress, and Gc, the critical energy release rate. The third parameter is the characteristic length l as in most of the strain gradient models. The proposed three-parameter model enables to take the different stress concentration levels into account, thus providing a criterion to predict fractures for any stress concentration, whether it is singular or not. Experimental results were selected to verify the accuracy and efficiency of the criterion. It was shown that the proposed model is physically reasonable, highly accurate, and easy to apply. It can be used in crack initiation prediction of engineering structures made of brittle materials.
LES of Wall-Bounded Flows Using a New Subgrid Scale Model Based on Energy Spectrum Dissipation
Authors: Veloudis I. , Yang Z. , McGuirk J. J.
Published: February 2008

A new one-equation subgrid scale (SGS) model that makes use of the transport equation for the SGS kinetic energy (kSGS) to calculate a representative velocity scale for the SGS fluid motion is proposed. In the kSGS transport equation used, a novel approach is developed for the calculation of the rate of dissipation of the SGS kinetic energy (ε). This new approach leads to an analytical computation of ε via the assumption of a form for the energy spectrum. This introduces a more accurate representation of the dissipation term, which is then also used for the calculation of a representative length scale for the SGS based on their energy content. Therefore, the SG length scale is not associated simply with the grid resolution or the largest of the SGS but with a length scale representative of the overall SGS energy content. The formulation of the model is presented in detail, and the new approach is tested on a series of channel flow test cases with Reynolds number based on friction velocity varying from 180 to 1800. The model is compared with the Smagorinsky model (1963, “General Circulation Experiments With the Primitive Equations: 1. The Basic Experiment,” Mon. Weather Rev., 91, pp. 90–164) and the one-equation model of Yoshizawa and Horiuti (1985, “A Statistically-Derived Subgrid Scale Kinetic Energy Model for the Large Eddy Simulation of Turbulent Flows,” J. Phys. Soc. Jpn., 54(8), pp. 2834–2839). The results indicate that the proposed model can provide, on a given mesh, a more accurate representation of the SG scale effects.
Dynamic Response of a Timoshenko Beam to a Moving Force
Authors: Śniady Paweł
Published: February 2008

We consider the dynamical response of a finite, simply supported Timoshenko beam loaded by a force moving with a constant velocity. The classical solution for the transverse displacement and the rotation of the cross section of a Timoshenko beam has a form of a sum of two infinite series, one of which represents the force vibrations (aperiodic vibrations) and the other one free vibrations of the beam. We show that one of the series, which represents aperiodic (force) vibrations of the beam, can be presented in a closed form. The closed form solutions take different forms depending if the velocity of the moving force is smaller or larger than the velocities of certain shear and bar velocities.
Analytical Solutions for a Family of Gaussian Impinging Jets
Authors: Xu Zhuyun , Hangan Horia , Yu Pei
Published: February 2008

Various types of impinging jet flows are analytically modeled using inviscid free Gaussian jet solutions superimposed with experimentally fitted boundary layer models. Improved (more robust) and simplified solutions to existing models are defined. Velocity profiles, surface pressure distributions, and streamline plots are calculated for circular, plane, and annular impinging jets. The models show excellent agreement with existing experimental results in both laminar and turbulent conditions and for different Reynolds numbers.
Discussion: “Exploring Effective Methods for Simulating Damaged Structures With Geometric Variation: Toward Intelligent Failure Detection” (McAdams, D. A., Comella, D., and Tumer, I. Y., 2007, ASME J. Appl. Mech., 74, pp. 191–202)
Authors: Whalen Timothy M.
Published: February 2008

The paper of McAdams et al. (ASME J. Appl. Mech. 74, pp. 191–202) explored two different approaches for damage detection in vibrating beams having both manufacturing variations in geometry and crack damage. One of the approaches, however, has a significant error in its formulation. The effects of this error on the formulation and the analytical results are discussed.
Multiscale Modeling of Adsorbed Molecules on Freestanding Microfabricated Structures
Authors: Begley Matthew R. , Utz Marcel
Published: February 2008

This paper outlines a multiscale model to quantitatively describe the chemomechanical coupling between adsorbed molecules and thin elastic films. The goal is to provide clear, quantitative connections between molecular interactions, adsorption distribution, and surface stress, which can be integrated with conventional thin film mechanics to quantify device performance in terms of molecular inputs. The decoupling of molecular and continuum frameworks enables a straightforward analysis of arbitrary structures and deformation modes, e.g., buckling and plate/membrane behavior. Moreover, it enables one to simultaneously identify both chemical properties (e.g., binding energy and grafting density) and mechanical properties (e.g., modulus and film geometry) that result in chemically responsive devices. We present the governing equations for scenarios where interactions between adsorbed molecules can be described in terms of pair interactions. These are used to quantify the mechanical driving forces that can be generated from adsorption of double-stranded DNA and C60 (fullerenes). The utility of the framework is illustrated by quantifying the performance of adsorption-driven cantilevers and clamped structures that experience buckling. We demonstrate that the use of surface-grafted polyelectrolytes (such as DNA) and ultracompliant elastomer structures is particularly attractive since deformation can be tuned over a very wide range by varying grafting density and chemical environment. The predictions illustrate that it is possible to construct (1) adsorption-based tools to quantify molecular properties such as polymer chain flexibility and (2) chemically activated structures to control flow in microfluidic devices.
Dynamic Crack Extension Along the Interface of Materials That Differ in Thermal Properties: Convection and Thermal Relaxation
Authors: Brock L. M.
Published: February 2008

Moving surface loads cause crack extension at a constant subcritical speed between perfectly bonded materials. The materials differ only in thermal properties and are governed by coupled thermoelastic equations that admit as special cases Fourier heat conduction and thermal relaxation with one or two relaxation times. Convection from the crack surfaces is allowed and for the latter two models is itself influenced by thermal relaxation. A dynamic steady state of plane strain is assumed. Fourier heat conduction is shown to dominate away from the crack edge at low speeds; solution behavior at the crack edge at high speeds depends upon the particular thermal model. Thermal mismatch is seen to cause solution behavior similar to that for the isothermal bimaterial, and so insight into the case of general material mismatch is provided.
Second-Order Diffraction Forces on an Array of Vertical Cylinders in Bichromatic Bidirectional Waves
Authors: Vazquez J. H. , Williams A. N.
Published: February 2008

A complete second-order solution is presented for the hydrodynamic forces due to the action of bichromatic, bidirectional waves on an array of bottom-mounted, surface-piercing cylinders of arbitrary cross section in water of uniform finite depth. Based on the constant structural cross section, the first-order problem is solved utilizing a two-dimensional Green function approach, while an assisting radiation potential approach is used to obtain the hydrodynamic loads due to the second-order potential. Results are presented which illustrate the influence of wave directionality on the second-order sum and difference frequency hydrodynamic forces on a two-cylinder array. It is found that wave directionality may have a significant influence on the second-order hydrodynamic forces on these arrays and that the assumption of unidirectional waves does not always lead to conservative estimates of the second-order loading.
Design Criteria for Offshore Structures Under Combined Wind and Wave Loading
Authors: Nessim M. A. , Hong H. P. , Swail V. R. , Henderson C. A.
Published: February 2008

Offshore codes do not give sufficient guidance regarding design criteria for loads resulting from combinations of stochastic environmental processes such as wind and waves. To assist design engineers in defining such criteria, a suite of methods that use environmental data to calculate the probability distributions of load effects resulting from combination of stochastic loads were investigated. An approach has been developed for using the results to calculate structure-specific and generalized load combination criteria. Extensive application of this approach in connection with Environment Canada’s wind and wave data bases for the Canadian East Coast region formed the basis for some interesting conclusions regarding the process of estimating combined extreme loads on offshore structures. It was found that data based on actual measurements of wave height and wind speed are preferable to hindcast data, since the latter have artificially high correlations that lead to overly conservative results. External analyses are most reliable when 20 or more years of data are used with analysis methods based on distribution tails. Reasonably good results can be achieved with 10 yr of data. Methods based on the point-in-time data and using mathematically convenient assumptions regarding distribution types and process characteristics can lead to large errors if the assumptions made are not substantiated by appropriate data. Load combination solutions are highly dependent on the geographic location and data base. Therefore, a separate analysis should be carried out for the structure and location being considered if possible. Wind and wave load combination solutions are sensitive to correlations and assumed distribution types; closed-form solutions for independent and Gaussian correlated processes can lead to significant errors. If site-specific analyses are not practical, companion action factors of 0.65, 0.60, and 0.55 for return periods of 20, 100, and 1000 yr, may be used for wind and wave loading on slender offshore structures in the Canadian East coast region. For wide structures in the same region, the suggested companion factors for the same return periods are 0.75, 0.70, and 0.65.
The Calculation of the Instability Criterion for a Uniform Viscous Flow Past an Oil Boom
Authors: Ertekin R. C. , Sundararaghavan H.
Published: February 2008

An important problem in oil spill containment by booms is the instability of the oil-water interface at the boom. This instability, which represents the conditions under which oil can escape under the boom, is investigated. A viscous flow model for thin slicks in two dimensions is developed. To understand the effect of viscosity on the instability criterion, the full Navier-Stokes equations are solved by the fractional-step method in time-domain to determine the pressure gradients along the boom. The numerically obtained viscous instability criterion Analytical instability formulas for potential flows are based on the velocity potentials for attached and detached flows due to uniform current past a flat plate in finite and infinite water depths. The results show that the viscous flow model predicts a larger region of stability. It is numerically determined from the instability criterion that the oil droplets at the boom between the free surface and down to about 40 percent of the boom height can never escape, regardless of the current strength. It is also shown that the instability criterion depends weakly on the high Reynolds number. Reanalysis of the available experimental data confirms these findings.
Active Control of Elastic and Rigid Body Response of a Three Dimensional Underwater Structure
Authors: Suzuki H. , Yoshida K. , Watanabe K.
Published: February 2008

One key technology for the offshore development of the increasing water depth will be remotely operated installation and construction of flexible structure in the deep water or on the seabed. The flexibility comes from scale-up or weight reduction of the structure. Conventional operation from the sea surface is affected by the weather conditions, and, therefore, not so efficient. This paper presents basic research on active control of elastic response and rigid body motion of an underwater elastic structure toward the remotely operated installation technique. The numerical model of the dynamics of the structural model is formulated, and based on the numerical model the control is formulated. The formulated control is tested by computer simulations and model experiments. The structural model is propelled by thrusters and taken from initial position to another position, while the elastic responses are controlled by variable buoyancy-type actuators.
Evaluation of Methods to Predict Safe Welding Conditions and Maximum HAZ Hardness in Steel Welding
Authors: Tronskar J. P.
Published: February 2008

During the last ten years new structural steels of improved weldability have been introduced. In particular, structural steels for the fabrication of offshore structures have been greatly improved in this respect throughout this period. These steels have lean chemical compositions which are generally outside the range for which the existing HAZ hardness criteria and the International Institute of Welding carbon equivalent (CEIIW) formula were originally developed. This paper presents the results from investigations of the weldability of three normalised (Re min 350 MPa) and three quenched and tempered (Re min 500 MPa) offshore structural steels. Weldability testing was conducted to study the relative performance of the different steels and to obtain a comparison between the capability of the different methods to predict safe welding conditions to avoid cold cracking in steel welding. It has become a widespread practice in welding high-strength steels to incorporate maximum HAZ hardness restrictions in fabrication specifications, particularly so in the offshore industry. Maximum HAZ hardness restrictions are often a point of contention between fabricators and their clients due to the difficulties often experienced in meeting these hardness requirements. Problems meeting maximum HAZ hardness requirements have been encountered for applications where maximum hardness HRC 22 or Vickers HV10 260 have been imposed for materials exposed to sour service in oil and gas production, processing and transportation. Many attempts have been made to develop empirical formulas for the estimation of maximum HAZ hardnesses. This paper presents some of the more successful approaches proposed to date and compares their performance.
Discussion of the Fatigue Crack Model Used as Decision Basis for Probabilistic Inspection Planning
Authors: Sigurdsson G. , Torhaug R.
Published: February 2008

Marine structures are often highly utilized structures and are operating in an environment dominated by dynamic loading. The fatigue limit state is of main concern and is governing the structural dimensions and the amount of resources utilized in inspection of several members and joints. There is a considerable uncertainty related to the parameters determining the fatigue life, and probabilistic analyses have therefore been used extensively in fatigue analysis. The models used both on describing the fatigue driving mechanisms and the deterioration mechanism, however, are always compromises between ability to describe nature and computational applicapability. In a state-of-the-art probabilistic fatigue analysis, major assumptions are made when establishing the crack growth model, such as: 1) the relation between membrane and bending stresses is assumed to be constant for all stress ranges, and one common stress component for the total stress is used to calculate fatigue crack growth. 2) The crack growth is assumed to follow a pattern with a constant relation between crack depth and crack length. This paper investigates the foregoing fundamental assumptions for the fatigue driving mechanism and shows the effect on time to the first inspection based on state-of-the-art probabilistic crack growth analysis for the detail of interest, for a simple but realistic jacket structure.
Damping of Resonant Oscillations of a Jacket Structure Based on Full-Scale Measurements
Authors: Thuestad T. C. , Nielsen F. G.
Published: February 2008

Damping of jacket structures are discussed on the basis of full-scale measurements. During a submarine impact with a jacket structure, unique transient response time series, damping properties are evaluated in terms of the nature and magnitude of the total damping. It is shown that the damping is highly nonlinear and fits a Coulomb-type model reasonably well. The damping magnitude expressed as the relative damping ratio is estimated to be in the range from 0.5 to 3.0 percent, dependent on the motion amplitude. Within the range of motion amplitudes experienced during the impact, the damping decreases with increasing motion amplitudes. The resonant motion amplitudes recorded during the impact are shown to be far greater than the expected dynamic motion amplitudes during a storm period.
Dynamic Response of a Single Flexible Cylinder in
Waves
Authors: Duggal A. S. , Niedzwecki J. M.
Published: February 2008

A large-scale experimental study to investigate the dynamic response of a single flexible cylinder in waves is presented. The cylinder was designed to exhibit the dynamic characteristics of a TLP riser or tendon in approximately 1000 m of water. Instrumentation provided detailed information on the inline and transverse curvature along the length of the cylinder. Wave loading mechanisms and the resulting response were investigated and compared with previous studies of rigid cylinders in oscillating flow. It was found that the complicated multifrequency response at large Keulegan-Carpenter numbers could be explained by introducing the depth dependence of the Keulegan-Carpenter number. The predicted inline response was shown to be reasonable for the wave frequency component of the measured inline response. Similarities between the measured transverse response and the high-frequency inline response were also shown. Probability density functions of the measured curvature were non-Gaussian, leading to significantly higher probabilities of curvature than would be predicted based on assuming a Gaussian process.
Nonlinear System Identification in Offshore Structural Reliability
Authors: Spanos P. D. , Lu R.
Published: February 2008

Nonlinear forces acting on offshore structures are examined from a system identification perspective. The nonlinearities are induced by ocean waves and may become significant in many situations. They are not necessarily in the form of Morison’s equation. Various wave force models are examined. The force function is either decomposed into a set of base functions or it is expanded in terms of the wave and structural kinematics. The resulting nonlinear system is decomposed into a number of parallel no-memory nonlinear systems, each followed by a finite-memory linear system. A conditioning procedure is applied to decouple these linear sub-systems; a frequency domain technique involving autospectra and cross-spectra is employed to identify the linear transfer functions. The structural properties and the force transfer parameters are determined with the aid of the coherence functions. The method is verified using simulated data. It provides a versatile and noniterative approach for dealing with nonlinear interaction problems encountered in offshore structural analysis and design.
Response of Short Cracks in High-Strength Steels to Fatigue Loadings—Part II: Behavior in Seawater Under Cathodic Polarization
Authors: Kim K. , Hartt W. H.
Published: February 2008

Experiments have been performed to determine the fatigue crack growth rate (FCGR) of short cracks (length from 0.1 to several mm) of five steels with yield stress in the range 370–570 MPa while cathodically polarized in natural seawater. Attention was focused on regions I and II of the classical FCGR-stress intensity range curve with particular consideration being given to the near-threshold behavior of short cracks. Single-edge notched, three-point bend specimens and a direct current potential drop crack monitoring system were employed; and test parameters were selected to simulate conditions experienced by deepwater offshore structures. These included a stress ratio of 0.5, a frequency of 0.3 Hz, and three levels of cathodic polarization (−800,−950, and −1100 mV, SCE). Crack growth rates were evaluated in terms of environment (air versus seawater), potential, material, and crack length. It was determined that cathodic polarization was generally beneficial with regard to FCGR compared to the freely corroding case, even at the most negative potential considered (−1100 mV, SCE), in contrast to what occurs for macro-cracks. The results are discussed within the context of design of offshore structures for resistance to fatigue.
Inelastic Response of a Deep Crack Single-Edge Notch Specimen Under
Impact Loading
Authors: Vargas P. M. , Dodds R. H.
Published: February 2008

Three-dimensional dynamic analyses are performed for a single-edge bend, SE(B), fracture specimen (a/W = 0.5) subjected to impact loading. Loading rates obtained in routine drop tower tests (terminal load-line velocity of 100 in./s or 2.54 m/s) are applied in the analyses. Explicit time integration coupled with an efficient element integration scheme is used to compute the dynamic response of the specimen. Strainrate sensitivity is introduced via a new, efficient implementation of the Bodner-Partom viscoplastic constitutive model. Material properties for A533B steel (a medium strength pressure vessel steel) are used in the analyses. Static analyses of the same SE(B) specimens provide baseline results from which inertial effects are assessed. Similarly, dynamic analyses using a strain-rate insensitive material provide a reference for the assessment of strain rate effects. Strains at key locations and the support reactions are extracted from the analyses to assess the accuracy of static formulas commonly used to estimate applied J values. In ertial effects on the applied J are quantified by examining the acceleration component of J. Results show that dynamic effects for the steel analyzed are negligible after twice a characteristic time that can be defined in terms of the first elastic period of the specimen.
Designing Shielded Metal Arc Consumables for Underwater Wet Welding in Offshore Applications
Authors: Sanchez-Osio A. , Liu S. , Olson D. L. , Ibarra S.
Published: February 2008

The use of underwater wet welding for offshore repairs has been limited mainly because of porosity and low toughness in the resulting welds. With appropriate consumable design, however, it is possible to reduce porosity and to enhance weld metal toughness through microstructural refinement. New titanium and boron-based consumables have been developed with which high toughness acicular ferrite (AF) can be produced in underwater wet welds. Titanium, by means of oxide formation, promoted an increase in the amount of acicular ferrite in the weld metal, while boron additions decreased the amount of grain boundary ferrite (GBF), further improving the microstructure. Porosity reduction was possible through the addition of calcium carbonate at approximately 13 wt percent in the electrode coating. However, weld metal decarburization also resulted with the addition of carbonate.
A Prediction of Dynamic Stresses for Long, Large-Diameter Horizontal Pipes at or Near the Ocean Free Surface
Authors: Nihous G. C.
Published: February 2008

A straight-beam approximation is applied to a long, stiff pipeline located at or near the ocean free surface. The analytical model determines vertical and horizontal transverse motions in a linear frequency-domain framework. Longitudinal dependence is expressed through a modal expansion, with the hydrodynamic loads calculated through slender-body theory. This method is validated by comparing predicted bending stresses for a 9.1-m-(30-ft-) dia pipe with corresponding model basin data. Maximum stresses occur when the wave angle allows a simultaneous matching of frequencies and projected wavelengths. Results also show peak stresses near the aft end of the pipe. Finally, it is confirmed that in deep water, bending stresses in the horizontal plane are in general smaller than those in the vertical plane.
Environmental Load Uncertainties for Offshore Structures
Authors: Nessim M. A. , Hong H. P. , Jordaan I. J.
Published: February 2008

A methodology for assessing the effect of different sources of uncertainty on the calculation of load effect on offshore structures is presented. A consistent classification of uncertainties was adopted and used as a basis to develop models to estimate the effect of different uncertainties on specified design loads. It is shown that distribution parameter uncertainties arising from limitations on the quantity of statistical data are not likely to have a significant effect on design loads. By contrast, model uncertainties can greatly increase the design loads, and the increase is sensitive to the probabilistic models used to describe model error. The methodology and results can be used by design engineers to take model uncertainties into account in estimating specified loads. They also form the basis for developing and calibrating a new information-sensitive code format.
Ship Hull Bottom Slamming
Authors: Rassinot P. , Mansour A. E.
Published: February 2008

A method is presented to evaluate the hull bending moment due to bottom slamming. Theoretical explanations and updates are given to the commonly used empirical results, and some observations are made on slamming. An energy approach combined with a strip theory is used to get the hydrodynamic load, and to analyze the effects of the forward velocity. Impacts of simple bodies are simulated numerically to describe these loads. The ship hull is represented as a nonuniform free-free beam, and its response is decomposed into normal modes; only the contribution of the first one is kept. In a numerical example, the bending moment during the impact is determined. It is shown that its value when the impact is over is much harder to predict. The maximum value of the bending moment, however, occurs during the impact, and is an increasing function of the vertical velocity, as expected. A simple expression is given for it.
Stress Concentration Factors of DK Square-to-Square Tubular Joints
Authors: Soh A.-K. , Soh C.-K.
Published: February 2008

The fatigue life of tubular joints with many braces, e.g., DK and DTK joints, are commonly determined by treating them as tubular joints with less braces, e.g., T/Y, K, and X joints, based on the joint classification approach recommended by the American Petroleum Institute. The DK square-to-square tubular joint type was selected to verify the reliability and accuracy of such an approach. A parametric stress analysis of DK square-to-square tubular joints subjected to axial loads, in-plane and out-of-plane bending moments has been performed using the finite element technique. The results of this analysis are presented as a set of formulas expressing the stress concentration factor as a function of the relevant geometric parameters for various loading conditions. A comparison is made between the results obtained for DK square-to-square tubular joints and those obtained for X and K square-to-square tubular joints, which are commonly employed to simulate the former when the joint classification approach is adopted. In general, the stress concentration factors for DK joints are significantly higher, which shows that the recommended approach may not be reliable and accurate in dealing with DK joints.
Uniaxial Constant Compressive Stress Creep Tests on Sea
Ice
Authors: Sinha N. K. , Zhan C. , Evgin E.
Published: February 2008

First-year columnar-grained sea ice from Resolute Passage (74° 42′ N, 94° 50′ W), off Barrow Strait in the Canadian High Arctic, was tested under constant uniaxial compressive stress applied normal to the length of the columns. Creep tests were performed at 263 K, 253 K, and 243 K in the stress range of 0.7 to 2.5 MPa, using prismatic samples with dimensions of 50 mm × 100 mm × 250 mm. Because three-dimensional creep data are extremely useful for developing constitutive equations, axial strain was measured in conjunction with the measurements of two lateral strains and acoustic emissions. The deformations were measured using displacement gages mounted on the samples. A description of the experimental procedures and the observations are presented here. One-to-one correspondence has been obtained between the present results on the dependence of minimum creep rate on stress and previous data on the dependence of uniaxial compressive strength on strain rate under constant strain rate. The strain-rate sensitivity of compressive strength can, therefore, be obtained from creep tests which can be performed by using simple dead-load test systems.
Uncertainty of Ocean Wave Hindcasts Due to Wind Modeling
Authors: Teixeira J. C. , Abreu M. P. , Guedes Soares C.
Published: February 2008

Two wind models were developed and their results were compared with data gathered during the Wangara experiment, so as to characterize their uncertainty. One of the models was adopted to generate the wind fields used as input to a second generation wave model. The relative error in the wind speed was considered in order to assess the uncertainties of the predictions or the significant wave height. Different time steps for the wind input were also used to determine their effect on the predicted significant wave height.
Floating Membrane Breakwater
Authors: Williams A. N.
Published: February 2008

The hydrodynamic properties of a flexible floating breakwater consisting of a membrane structure attached to a small float restrained by moorings are investigated theoretically. The tension in the membrane is achieved by hanging a clump weight from its lower end. 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 membrane of uniform mass per unit length subjected to a constant axial force. The boundary integral equation method is applied to the fluid domain, and the dynamic behavior of the breakwater is also described through an appropriate Green function. Numerical results are presented which illustrate the effects of the various wave and structural parameters on the efficiency of the breakwater as a barrier to wave action. It is found that the wave reflection properties of the structure depend strongly on the membrane length, the magnitude of the clump weight, and the mooring line stiffness, while the membrane weight and excess buoyancy of the system are of lesser importance.
Offshore North Sea Pipeline and Riser Loss of Containment Study
(PARLOC)—Applications and Limitations in the Assessment of Operating
Risks
Authors: Robertson J. L. M. , Smart D. , Al-Hassan T.
Published: February 2008

Since the Piper Alpha disaster in 1988, there has been an urgent requirement to prevent such tragedies occurring by the introduction of higher safety standards and by improving the confidence in the statistical information available for the assessment of the risks of loss of containment associated with operation of North Sea pipelines. In order to achieve the latter, two databases have been compiled: 1) a pipeline database containing details of pipelines and risers installed in the North Sea; 2) an incident database containing details of reported “occurrences” (covering the period from 1975 to end 1993), which directly resulted or threatened to result in loss of containment from a pipeline or riser. The data has been compiled from information obtained from: U.K., Norwegian, Dutch and Danish Regulatory Authorities; Operators in the U.K., Dutch and Danish Sectors; reports from previous studies made available to the study; published sources. The databases have been used to perform assessments of factors affecting the frequency of incidents, such as: incident cause; part of pipeline or riser affected; pipeline or riser diameter, length, contents, age, type; whether the line is trenched or buried, piggy-backed or not; hydrotest pressure; location of pipeline or riser in the North Sea. The PARLOC study identifies potential hazards and provides an indication of likely loss of containment frequency associated with the operation of North Sea pipelines and risers. Furthermore, PARLOC provides a continually updated key reference for comparative risk assessment and ultimately for the implementation of risk control as part of an overall risk management program.
Welding Residual Distortions in Ring-Stiffened Pipes
Authors: Josefson B. L. , Wikander L. O. , Hederstierna J. F. , Johansson F. K.
Published: February 2008

A fast and simple method for the determination of the residual deformation for a class of welding problems, ring-stiffened pipes, is proposed. The method can predictradial as well as angular distortion of the thin-walled pipe-ring-stiffener/flange assembly. The pipe and stiffener material is elasto-plastic. In particular, the accumulation of deformation in multipass welding is incorporated in the model. Each weld pass is treated separately. This facilitates the assessment of the influence of the sequence in which the weld passes are deposited on the residual deformation state. The method will be included in a conversational knowledge-based “expert” system for the production of a welded ring-stiffened pipe.
Fracture Toughness of Freshwater Ice—Part I: Experimental Technique
and Results
Authors: Weber L. J. , Nixon W. A.
Published: February 2008

Experiments have been performed to determine the effect of loading rate and temperature on the fracture toughness of both granular and S2 columnar freshwater ice. Loading rate was varied from 0.04 to 40.0 kPam s-1, and over this range the fracture toughness was observed to decrease from 201 to 109 kPam. Examination of load—CMOD curves indicate that at a loading rate of 40 kPam s-1, the crack tip plasticity was sufficiently limited that the specimen behavior can be considered linear elastic, thus providing a valid Kq measurement. When test temperature was varied from −5 to −45°C for the S2 columnar ice, no significant variation in toughness was observed. In contrast, for granular ice, a higher toughness (144 kPam) was observed in the −5 to −20°C range than for the S2 columnar ice. However, the toughness of the granular ice at−45°C is not significantly different from that of the S2 columnar ice. A companion paper (Weber and Nixon, 1996) analyzes the results in greater detail comparing them with previous work, and presents a detailed fractographic analysis of the failure surfaces.
Fracture Toughness of Freshwater Ice—Part II: Analysis and
Micrography
Authors: Weber L. J. , Nixon W. A.
Published: February 2008

Experiments have been performed to determine the effect of loading rate and temperature on the fracture toughness of freshwater ice. A first paper (Weber and Nixon, 1996) presents the experimental technique and results, while this paper focuses on discussion of the crack tip process zone and fracture surface micrography. A simple method to estimate the size of the process zone will be presented. Also, fracture surface micrography will be used to interpret the results of the temperature experiments by considering evidence of dislocation activity in preferentially oriented grains.
The Propagation of Wind Errors Through Ocean Wave
Hindcasts
Authors: Holthuijsen L. H. , Booij N. , Bertotti L.
Published: February 2008

To estimate uncertainties in wave forecast and hindcasts, computations have been carried out for a location in the Mediterranean Sea using three different analyses of one historic wind field. These computations involve a systematic sensitivity analysis and estimated wind field errors. This technique enables a wave modeler to estimate such uncertainties in other forecasts and hindcasts if only one wind analysis is available.
Spectral Fatigue Analysis of Shallow Water Jacket
Platforms
Authors: Bishop N. W. M. , Feng Q. , Schofield P. , Kirkwood M. G. , Turner T.
Published: February 2008

The spectral analysis approach is a very elegant and computationally efficient method of analyzing the fatigue life of offshore jacket platforms. The primary limitation of the approach is that it assumes linearity of both the structural system and the wave-loading mechanism. The approach is now widely used for the analysis of deepwater, dynamically responsive platforms where nonlinearities are usually not serious. There are also advantages associated with using the approach for shallow water platforms although nonlinearities then become significant, particularly the wave-loading mechanism. Various methods have been proposed to enable the spectral method to be used for some nonlinear situations, including a new approach which uses the Longuet-Higgins wave height-period joint probability density function in order to obtain a better linearization technique. This linearization process is associated with the particular wave heights chosen for producing the transfer functions. The new approach provides a better method for choosing the appropriate height of each so-called base wave case. In order to verify the new approach, a time series analysis, including wave-loading nonlinearities, has been adopted to obtain a reference fatigue life. The sea surface elevation spectrum has been decomposed into a set of equivalent harmonic components. The water particle velocities and accelerations were then individually evaluated and the appropriate (Morison’s) wave loading was computed for each time step in the sea surface time history. The structural stress response time history was then calculated, from which a fatigue life estimate was obtained. This paper presents the results obtained using this new approach, as well as comparative results obtained using the deterministic, spectral, and time domain approaches applied with a representative sea state. The results show that the deterministic-spectral method has a considerable amount of potential, especially for new design work where weight savings and/or increased confidence levels may be achieved.