bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of dental care on oral health‐related quality of life and treatment goals among elderly adults
Authors: Gagliardi DI , Slade GD , Sanders AE
Published: February 2008

Background:  General dental care can effectively control disease and restore damaged tissue, yet little is known about its impact on patients’ subjective oral health, namely treatment goals and oral health‐related quality of life (OHRQoL). This study aimed to evaluate change in both aspects of subjective oral health among elderly adults receiving publicly‐funded, general dental care.

Methods:  We conducted a prospective, single‐group intervention study of adults aged 75+ years receiving care through the South Australian Dental Service (SADS). Before receiving dental care, subjects completed the Oral Health Impact Profile (OHIP‐14) questionnaire which evaluates OHRQoL. In this questionnaire, subjects rated the extent to which they had attained a self‐nominated oral health goal. Dentists provided standard‐of‐care treatment and six months later the OHIP‐14 and goal attainment questions were re‐administered.

Results:  Among the 253 adults studied, overall improvements in OHRQoL were observed (p < 0.05), although the effect was dependent on pre‐treatment goal: mean OHIP‐14 scores did not change significantly for subjects whose goal was less pain/discomfort while significant improvements were observed for subjects with other treatment goals. In contrast, mean goal attainment ratings improved significantly (P < 0.05), regardless of treatment goal categories.

Conclusions:  Dental care was associated with improvements in subjective oral health, although different patterns of improvement were observed for OHRQoL compared with goal attainment ratings.
Parental knowledge, beliefs and behaviours for oral health of toddlers residing in rural Victoria
Authors: Gussy MG , Waters EB , Riggs EM , Lo SK , Kilpatrick NM
Published: February 2008

Background:  Little is known about the oral health of children under the age of four years. The determinants of early childhood caries (ECC) in this young age group are also not well understood despite a growing recognition that early interventions may deliver the greatest benefits. The aim of this study was to examine the oral health‐related knowledge, attitudes and reported behaviours of parents of children aged 12–24 months living in rural areas of Victoria, Australia.

Methods:  A robust theoretical model was utilized to identify oral health‐related behaviours and their antecedent and reinforcing conditions within the context of this specific population group. Two hundred and ninety‐four parent/child dyads were recruited through their maternal and child health nurses as part of a larger intervention trial. Parents completed a self‐report questionnaire.

Results:  Knowledge regarding risk and protective factors amongst parents was variable and sometimes at odds with contemporary evidence. Knowledge of the role of early infection with S. mutans was very low, with high levels of behaviours that may promote early transmission reported. Tooth cleaning was reported by most parents at least sometimes, however a large proportion lacked confidence and this was significantly related to the frequency of the cleaning. Parents were confused about the fluoride status of their water supplies. Most parents believed fluoride toothpaste reduced the risk of ECC but did not know whether it should be used with toddlers.

Conclusions:  The results of this study have implications for efforts to prevent dental decay in this very young age group. Health care professionals other than dentists need support to provide information and promote confidence with regard to optimal fluoride exposure. Attention should also be given to the contribution of early contact with particular bacteria in oral health education and promotion programmes.
Attitudes of the Victorian oral health workforce to the employment and scope of practice of dental hygienists
Authors: Hopcraft M , McNally C , Ng C , Pek L , Pham TA , Phoon WL , Poursoltan P , Yu W
Published: February 2008

Background:  Increasing the number of dental hygienists and expanding their scope of practice are two policy directions that are currently being explored to increase the supply of dental services in the context of projected oral health workforce shortages in Australia. Understanding factors relating to the employment of hygienists and the attitudes of the oral health workforce to dental hygiene practice are important in this policy debate.

Methods:  A postal survey of a random sample of Victorian dentists, periodontists, orthodontists and hygienists was undertaken in 2006. Dentists and specialists were grouped into those whose practice employed or did not employ a hygienist. Data on the attitudes of dentists, specialists and hygienists towards various aspects of dental hygiene practice were explored.

Results:  A response rate of 65.3 per cent was achieved. Hygienists believed that their employment made dental care more affordable (53.7 per cent) and improved access to dental care (88.1 per cent), while few dentists believed hygienists made care more affordable. Most hygienists believed they were capable of diagnosing periodontal disease and dental caries and formulating a treatment plan, but there was less support from employers and non‐employers. Dentists were strongly opposed to independent practice for dental hygienists, although there was qualified support from employers for increasing the scope of practice for hygienists.

Conclusions:  Dentists who worked with hygienists acknowledged their contribution to increasing practice profitability, efficiency and accessibility of dental services to patients. Hygienists and employers supported increasing the scope of dental hygiene practice, however the majority of non‐employers opposed any expansion.
What Am I? Virtual Machines and the Mind/Body Problem
Authors: POLLOCK JOHN L.
Published: February 2008

When your word processor or email program is running on your computer, this creates a “virtual machine” that manipulates windows, files, text, etc. What is this virtual machine, and what are the virtual objects it manipulates? Many standard arguments in the philosophy of mind have exact analogues for virtual machines and virtual objects, but we do not want to draw the wild metaphysical conclusions that have sometimes tempted philosophers in the philosophy of mind. A computer file is not made of epiphenomenal ectoplasm. I argue instead that virtual objects are “supervenient objects.” The stereotypical example of supervenient objects is the statue and the lump of clay. To this end I propose a theory of supervenient objects. Then I turn to persons and mental states. I argue that my mental states are virtual states of a cognitive virtual machine implemented on my body, and a person is a supervenient object supervening on this cognitive virtual machine.
Wright on the McKinsey Problem
Authors: BRUECKNER ANTHONY
Published: February 2008

The McKinsey Problem concerns a puzzling implication of the doctrines of Content Externalism and Privileged Access. I provide a categorization of possible solutions to the problem. Then I discuss Crispin Wright’s work on the problem. I argue that Wright has misconceived the status of his own proferred solution to the problem.
‘Boundary blowup’ type sub‐solutions to semilinear elliptic equations with Hardy potential
Authors: Bandle Catherine , Moroz Vitaly , Reichel Wolfgang
Published: February 2008

Semilinear elliptic equations which give rise to solutions blowing up at the boundary are perturbed by a Hardy potential μ/δ(x, ∂Ω)2, where δ(x, ∂Ω) denotes the distance function. The size of this potential affects the existence of a certain type of solutions (large solutions): if μ is too small, then no large solution exists. The presence of the Hardy potential requires a new definition of large solutions, following the pattern of the associated linear problem. Nonexistence and existence results for different types of solutions will be given. Our considerations are based on a Phragmen–Lindelöf type theorem which enables us to classify the solutions and sub‐solutions according to their behavior near the boundary. Nonexistence follows from this principle together with the Keller–Osserman upper bound. The existence proofs rely on sub‐ and super‐solution techniques and on estimates for the Hardy constant derived by Marcus, Mizel and Pinchover [Trans. Amer. Math. Soc. 350 (1998) 3237–3255].
Spectral Stiffness Microplane Model for Quasibrittle Composite Laminates—Part II: Calibration and Validation
Authors: Beghini Alessandro , Cusatis Gianluca , Bažant Zdeněk P.
Published: February 2008

The spectral stiffness microplane (SSM) model developed in the preceding Part I of this study is verified by comparisons with experimental data for uniaxial and biaxial tests of unidirectional and multidirectional laminates. The model is calibrated by simulating the experimental data on failure stress envelopes analyzed in the recent so-called “World Wide Failure Exercise,” in which various existing theories were compared. The present theory fits the experiments as well as the theories that were best in the exercise. In addition, it can simulate the post-peak softening behavior and fracture, which is important for evaluating the energy-dissipation capability of composite laminate structures. The post-peak softening behavior and fracture are simulated by means of the crack band approach which involves a material characteristic length.
Stability of SDOF Linear Viscoelastic System Under the Excitation of Wideband Noise
Authors: Huang Qinghua , Xie Wei-Chau
Published: February 2008

The moment Lyapunov exponents of a single degree-of-freedom viscoelastic system under the excitation of a wideband noise are studied in this paper. A realistic example of such a system is the transverse vibration of a viscoelastic column under the excitation of stochastic axial compressive load. The method of averaging, both first order and second order, is applied. The averaged Itô differential equation governing the pth norm is established and the pth moment Lyapunov exponent is then obtained. White noise and real noise are considered as models of wideband noises. The variations of the moment Lyapunov exponents with the change of different parameters are discussed.
Elastic Boundary Layers in Two-Dimensional Isotropic Lattices
Authors: Phani A. Srikantha , Fleck Norman A.
Published: February 2008

The phenomenon of elastic boundary layers under quasistatic loading is investigated using the Floquet–Bloch formalism for two-dimensional, isotropic, periodic lattices. The elastic boundary layer is a region of localized elastic deformation, confined to the free edge of a lattice. Boundary layer phenomena in three isotropic lattice topologies are investigated: the semiregular Kagome lattice, the regular hexagonal lattice, and the regular fully triangulated lattice. The boundary layer depth is on the order of the strut length for the hexagonal and the fully triangulated lattices. For the Kagome lattice, the depth of boundary layer scales inversely with the relative density. Thus, the boundary layer in a Kagome lattice of low relative density spans many cells.
Modeling Surface Electrodes on a Piezoelectric Layer
Authors: Wang B.-L. , Mai Y.-W.
Published: February 2008

This paper considers a piezoelectric ceramic layer with a surface electrode. It focuses on the effect of the layer thickness on the electrode tip fields. A closed-form solution for the electromechanical fields at the electrode tip is obtained and is expressed in terms of the applied electric field intensity factor, which can be obtained exactly for infinite layer thickness and numerically for finite layer thickness. The stress, electric displacement, and electric field are plotted to show the effect of layer thickness. It is found that the stresses and field intensities at the electrode tip can be reduced considerably by decreasing the thickness of the piezoelectric layer, confirming the previous finding. The paper also gives a solution for two identical and collinear surface electrodes. The relative distance between the electrodes is observed to have significant influence on the electromechanical field in the piezoelectric layer.
Anomalous Frictional Behavior in Collisions of Thin Disks Revisited
Authors: Mourya Rahul , Chatterjee Anindya
Published: February 2008

In prior work, Calsamiglia et al. (1999, “Anomalous Frictional Behavior in Collisions of Thin Disks,” ASME J. Appl. Mech., 66, pp. 146–152) reported experimental results of collisions between thin plastic disks and a relatively rigid steel barrier. In those experiments, it was observed that, contrary to a commonly held assumption in rigid body collision modeling, the ratio of tangential to normal components of the contact impulse could be substantially less than the friction coefficient even for collisions where the disk contact point did not reverse its velocity direction (i.e., for sliding collisions). In those experiments, the disk’s edges were rounded to make the contact less sensitive to machining imperfections. While such impact/contact is nominally at a single point, the rounded edges make the interaction three dimensional (from the view point of analyzing deformations). Here, we revisit that problem computationally, but model the edges as flat, making the problem two dimensional. Our finite element calculations (ABAQUS) do not reproduce the anomalous frictional interactions observed in those experiments, suggesting that rounding of the edges, among other possibilities, may have played a significant role in the experimental results.
Synchronization of Multiple Chaotic Gyroscopes Using the Fundamental Equation of Mechanics
Authors: Udwadia Firdaus E. , Han Byungrin
Published: February 2008

This paper provides a simple, novel approach for synchronizing the motions of multiple “slave” nonlinear mechanical systems by actively controlling them so that they follow the motion of an independent “master” mechanical system. The multiple slave systems need not be identical to one another. The method is inspired by recent results in analytical dynamics, and it leads to the determination of the set of control forces to create such synchronization between highly nonlinear dynamical systems. No linearizations or approximations are involved, and the exact control forces needed to synchronize the nonlinear systems are obtained in closed form. The method is applied to the synchronization of multiple, yet different, chaotic gyroscopes that are required to replicate the motion of a master gyro, which may have a chaotic or a regular motion. The efficacy of the method and its simplicity in synchronizing these mechanical systems are illustrated by two numerical examples, the first dealing with a system of three different gyros, the second with five different ones.
Bifurcations of Equilibria in Potential Systems at Bimodal Critical Points
Authors: Mailybaev Alexei A. , Seyranian Alexander P.
Published: February 2008

Bifurcations of equilibria at bimodal branching points in potential systems are investigated. General formulas describing postbuckling paths and conditions for their stability are derived in terms of the original potential energy. Formulas describing unfolding of bimodal branching points due to a change of system parameters are given. A full list of possible cases for postbuckling paths, their stability, and unfolding depending on three system coefficients is presented. In order to calculate these coefficients, one needs the derivatives of the potential energy and eigenvectors of the linearized problem taken at the bifurcation point. The presented theory is illustrated by a mechanical example on stability and postbuckling behavior of an articulated elastic column having four degrees of freedom and depending on three problem parameters (stiffness coefficients at the hinges). For some of the bimodal critical points, numerical results are obtained illustrating influence of parameters on postbuckling paths, their stability, and unfolding. A surprising phenomenon that a symmetric bimodal column loaded by an axial force can buckle with a stable asymmetric mode is recognized. An example with a constrained sum of the stiffnesses of the articulated column shows that the maximum critical load (optimal design) is attained at the bimodal point.
Development of Component-Level Damage Evolution Models for Mechanical Prognosis
Authors: Haroon Muhammad , Adams Douglas E.
Published: February 2008

This paper presents component-level empirical damage evolution regression models based on loads and damage information that do for mechanical damage prediction what the Paris law does for predicting crack growth under fatigue loading. Namely, these regression models combine information about the current damage state and internal system loads to predict the progress of damage to failure. One of the drawbacks of Paris-like crack evolution laws is that localized information about the loading (stress) and damage (crack length) is required. In structural health monitoring applications, it is not feasible to instrument every potential crack initiation region to collect this localized information. The component-level damage evolution regression models developed here only require global measurements that quantify the damage and loading at the level of the component rather than at the site of damage. This paper develops damage evolution regression models for an automotive sway bar link undergoing axial fatigue loading with two different damage mechanisms at a weldment and at an electrical discharge machining notch. Restoring force diagrams are used to calculate the load indicators as damage progresses and transmissibility functions are used to calculate the damage indicator during tests to failure. A component-level load intensity factor (ΔK) is calculated during these tests so that the rate of damage accumulation can be used to predict the growth of damage and ultimate failure.
Indentation and Splitting of Freshwater Ice Floes
Authors: Sodhi D. S. , Chin S. N.
Published: February 2008

Small-scale indentation and floe-splitting experiments were conducted on columnar ice floes of various sizes and at different speeds. During low-speed indentation (0.2–8 mm s−1), the ice floes always split apart, while at higher indentation speeds (> 100 mm s−1) they did not. The reason is attributed to differences in the process of deformation and failure. At low speed, a large zone of microcracked ice forms in front of the indentor. Development of compressive stresses in the microcracked ice zone leads to buildup of transverse forces that drive crack propagation. These zones of microcracked ice are not observed during high-speed indentation. Rather, the ice fails by continuous crushing. The theoretical effective pressure required to split an ice floe, as predicted by Bhat (1988), agrees to some extent with those measured during experiments.
Fatigue of Drill String Connections
Authors: Brennan F. P.
Published: February 2008

This paper reports full-scale tests on threaded connections used in drill strings. A concise background is given concerning the in-service environment and loading conditions on the connections. This details some of the reasons particular steels are used in preference to others. Crack growth data is given for ten full-scale axial and rotating bend tests. This is compared with predictions from a dedicated weight function fracture mechanics solution designed for threaded connections. Crack aspect ratio is considered with a view to development of an appropriate empirical model.
Effects of CG Location on the Launch Behavior of Free-Fall
Lifeboats
Authors: Nelson J. K. , Fallon D. J. , Hirsch T. J.
Published: February 2008

The free-fall lifeboat was developed to reduce the risk of injury during evacuation in a maritime emergency. It is a generally accepted concept for lifesaving appliances that currently is in use on many ships and offshore platforms. Three concerns during launch of these lifeboats are the attitude of the boat at water entry, the headway immediately after water entry, and the acceleration forces to which the occupants are subjected. Limited quantitative data is available about the behavior of the boats during launch and, in particular, on the effects of mass distribution on the launch behavior of free-fall lifeboats. The purpose of this paper is to discuss quantitatively the launch behavior of free-fall lifeboats, with particular emphasis on the effects of changes in the location of the CG.
Simulation of Time Histories of Second-Order Wave Effects by
Pseudo-Linear Transformation
Authors: Li Y.
Published: February 2008

Simulation of the time histories of second-order wave effects is often performed by quadratic transformation of a wave time history. By the present approach, the quadratic transformation of waves is approximated by linear combinations of the products of component wave time records and their Hilbert transforms. The computational efficiency is greatly enhanced. The efficient quadratic transformation of a time history is for the time domain solution of structural dynamic response, and can also be used as a post-processor of the frequency domain solution for obtaining statistic parameters of dynamic response.
Quickwave: An Impulse Algorithm to Calculate Preliminary Design Shear
and Moment Envelopes for Compliant Towers
Authors: Morrison D. G.
Published: February 2008

A novel, simple method to calculate compliant tower (CT) level shear and moment envelopes for preliminary design has been developed, and verified by comparing with rigorous 3-D tower analyses. The approach relies on a vast experience base to define important features influencing the dynamic response of CTs, and a new closed-form solution for the acceleration (needed to construct design envelopes) of the tower caused by an impulsive-type wave load. The main benefits of the approach are: 1) the designer can iterate and quickly converge on a working preliminary design without resorting to time-consuming computer analyses; 2) the designer can quickly evaluate configurations for different water depths, pile arrangements, payload, steel grade, reserve buoyancy, and well counts.
Comparative Study of Joint Distributions of Primary Wave
Characteristics
Authors: Myrhaug D. , Kva˚lsvold J.
Published: February 2008

A comparative study of joint distributions of wave height and period, as well as wave height and steepness, is presented. The analysis includes two theoretical joint distributions of wave height and wave period. These two distributions are transformed into joint distributions of wave height and wave steepness. The theoretical distributions are compared with measured data, as well as parametric models which are obtained by fitting to the data. The data used for comparison are relatively broad-banded and are obtained from measurements in deep waters on the Norwegian continental shelf. It is found that the theoretical distributions are inadequate to describe the joint distributions of the primary wave characteristics of these broad-band data, and thus it is suggested to use parametric models to describe such data. Finally, the engineering relevance of the joint distribution of wave height and wave steepness is discussed.
Response Statistics of Moored Offshore Structures
Authors: Kinoshita T. , Takase S.
Published: February 2008

This paper discusses the prediction of extreme values for total first and second-order responses of a floating structure moored in random seas. It is hard to estimate the extreme values from time series simulation or experimental data of limited length. Several methods of theoretical estimation of the extreme values are examined. They are the SRSS formula introduced by Naess (1987, 1989), the modified SRSS with a correlation parameter, the SRSS with Naess (1987, 1989) corection factor, the approximate SRSS (Naess, 1989), and the formula proposed by authors previously. The results of those methods are compared, and it is confirmed that the last one is very promising.
Non-Gaussian Noise Effects on Reliability of Multistable Systems
Authors: Simiu E. , Grigoriu M.
Published: February 2008

For certain types of compliant structures, the designer must consider limit states associated with the onset of fluidelastic instability. These limit states may include bifurcations from motion in a safe region of phase space to chaotic motion with exits (jumps) out of the safe region. In practice, such bifurcations occur in systems with noisy or stochastic excitations. For a wide class of dynamical systems, a fundamental connection between deterministic and stochastic chaos allows the application to stochastic systems of a necessary condition for the occurrence of chaos originally obtained by Melnikov for the deterministic case. We discuss the application of this condition to obtain probabilities that chaotic motions with jumps cannot occur in multistable systems excited by processes with tail-limited marginal distributions.
Response of Short Cracks in High-Strength Steels to Fatigue Loadings—Part I: Behavior in Air and Freely Corroding in Seawater
Authors: Kim K. , Hartt W. H.
Published: February 2008

Experiments have been performed which determined the growth rate of short cracks (initial depth ~ 0.1 mm) for five high-strength steels (yield stress 370–570 MPa) in air and natural seawater. Attention was focused on regions I and II of the classical da/dN-ΔK curve with test conditions being relevant to offshore structure service. The results indicated enhanced growth rate for short fatigue cracks (a ⪝ 1 mm) in both environments. Parameters with which short crack fatigue behavior might best be correlated were investigated, and it was found that the enhanced fatigue crack growth rate associated with short cracks transitioned to long crack growth kinetics at a ΔK value which depended only upon environment. The significance of the results are discussed within the context of offshore structure integrity.
Hydrodynamic Damping, Flow-Induced Oscillations, and Biharmonic Response
Authors: Sarpkaya T.
Published: February 2008

A brief review of damping is followed by a comparison of three sets of lift-force data for circular cylinders, subjected only to transverse oscillation. Then the significance of two-dimensional or biharmonic oscillations (in both the in-line and transverse directions) is discussed in light of experiments undertaken for that purpose, to simulate more closely the true nature of flow-induced oscillations.
Crack Interaction Criteria in Pressure Vessels and Pipe
Authors: Kim D. S. , Lo K. H.
Published: February 2008

An attempt was made to define a new crack interaction criterion for pressurized cylinders with two co-planar surface cracks. Elastic-plastic finite element method with line spring concept (line spring element method) was used to verify the validity of the new interaction criterion and to establish the relative conservatism built into various codes/standards. The crack interaction criteria of two co-planar surface cracks as defined by ASME Section XI and BS PD6493 were studied and a new interaction criterion which accounts for crack shape and load factor was introduced. The basic idea behind the crack interaction criteria for co-planar surface cracks was the plastic zone and stress interaction near crack tips. To verify the new crack interaction criterion, comparisons of J-integral values were made for various crack sizes with different distances between cracks and loading conditions. Based upon these comparisons, the new crack interaction criteria, comparing a physical distance, s, to a characteristic distance d=(σ/σy)2(c1Q1 + c2Q2), proved to be a reasonable parameter for indication of the crack driving force interaction for co-planar cracks. The characteristic distance also represents a rigorous measure of an equivalent crack driving force for interacting cracks.
The Flow Properties of Crushed Ice
Authors: Singh S. K. , Jordaan I. J. , Xiao J. , Spencer P. A.
Published: February 2008

The flow properties of crushed ice under plane-strain conditions are examined. The analysis is based on a set laboratory experiments. The geometric configuration provided a wide range of pressures and material behaviors. At the early stages of the extrusion, and near the exit, where pressures are low, models based on Mohr-Coulomb flow theory describe the extrusion of crushed ice satisfactorily. At more advanced stages of the tests, high pressures developed, crushed ice became fused, and its behavior was similar to that of highly damaged polycrystalline ice. An extrusion model based on a nonlinear viscous flow is presented. This formulation is appropriate for the pressure ranges encountered in ice-structure interaction. After the initial compaction of the material, the dynamic force characteristics similar and cracking are not necessary to produce the dynamic effect in the ice-structure interaction. The vibrations appear to be related to variations in the width of the fused zone of ice.
On the Hydrodynamic Design of Active Panels of Marine Vehicles
Authors: McCormick M. E. , Mouring S. E.
Published: February 2008

The problem of active, or driven, panel motions of marine vehicles altering the turbulent boundary layer properties is discussed. The coherent (vorticular) structures in a turbulent boundary layer can be altered by the motions of a panel causing those structures to grow more rapidly and, as a result, become prematurely unstable and burst. In addition, the motions of the panel can produce vortices that interact with those that are naturally produced, and change the character of the boundary layer. The motions of the antinodes of the panel can also increase or decrease the surface shear stress, if the panel is, respectively, above or below its mean position. The cumulative effect of the active-panel motions, then, could be to increase the boundary layer drag. An outline of the analysis of this phenomenon is presented.
Oscillating Flow About Two and Three-Dimensional Bilge
Keels
Authors: Sarpkaya T. , O’Keefe J. L.
Published: February 2008

The paper describes an experimental investigation of the damping provided by bilge keels in an oscillating flow (in a large U-shaped water tunnel). Rectangular and square flat plates were placed adjacent to a solid boundary (with no gap) in order to simulate flow about bilge keels. The single free edge of the rectangular plate and the three free edges of the square plates were beveled to 60-deg angles so as to form sharp edges with included angles of about 60 deg. For comparison, another sharpedged rectangular plate was tested without the wall proximity effects. All plates were held normal to the direction of the ambient flow. The Fourier-averaged drag and inertia coefficients were then calculated as a function of a suitable Keulegan-Carpenter number through the use of the instantaneous force acting on each plate.
A Methodology for Modeling Lift as a Modulated
Process
Authors: Longoria R. G.
Published: February 2008

This paper presents a methodology for using a modulated process to model the lift forces induced on circular cylinders by an oscillating flow. The generalization of the existing quasi-steady flow model leads to techniques which apply the Hilbert transform in model evaluation and parameter determination. Analysis of measured lift forces reveals clearly identifiable forms of amplitude and angle modulation, justifying the use of a modulation model. As a demonstration, a method is presented for evaluating the quasi-steady flow model and for determining model parameters using data obtained under both periodic and random flow conditions. Although empirical in nature, modulation models can reproduce critical characteristics of lift forces such as frequency content, amplitude, and zero-crossings. It is suggested that the Hilbert transform can facilitate model development and evaluation beyond the simple quasisteady form. Further, the methodology employed can be used in characterizing any physical process exhibiting amplitude and/or angle modulation.
Markov Description of Wave-Crest Statistics
Authors: Dawson T. H. , Kriebel D. L. , Wallendorf L. A.
Published: February 2008

Markov description of wave-crest statistics is considered for the case of severe random seas where Stokes nonlinearities require crests to rise higher than troughs fall. Of interest are the average number of consecutive high waves in runs of high waves and the average number of waves between beginnings of such runs, with high waves being defined in terms of a threshold level above mean water level. Two basic parameters are involved in the description: 1) the probability P that a high wave will occur at a fixed location, and 2) a coefficient C relating P to the probabilities associated with transitions from high to low waves and low to high waves. Comparison with laboratory measurements from scaled Bretschneider seas having a range of nonlinearities indicates that the basic Stokes nonlinearity is contained in the probability P, with no sensible dependence exhibited by the coefficient C. Additional comparison with scaled Jonswap seas illustrates the dependence of this coefficient on spectral shape. A final consideration of results from full-scale hurricane sea conditions, and from corresponding scaled laboratory data, demonstrates the general applicability of the laboratory results presented here to actual wind-driven seas.
Overlapped K Joints in Circular Hollow Sections Under Axial Loading
(An Investigation of the Factors Affecting the Static Strength Using Numerical
Modeling)
Authors: Dexter E. M. , Lee M. M. K. , Kirkwood M. G.
Published: February 2008

Overlapped joints are generally regarded as having higher strengths than otherwise identical, simple nonoverlapping joints because of the more efficient load transfer between braces. However, not only that relatively little research has been carried out on such joints, the few test data from which current design guidance was derived has also been recently rejected. This paper reports the first phase of a parametric finite element study into the strength of overlapping K joints under axial loading. The numerical models were validated and calibrated against existing gap and overlapped K joint test results, and various factors which affect the relationship between the strength and the overlap amount, such as boundary restraints, hidden welds, loading hierarchy, and failure modes, were investigated. The results of the work presented lay the foundation for a future parametric study.
A Study on Buckling of Offshore Pipelines
Authors: Chiou Y.-J. , Chi S.-Y.
Published: February 2008

The beam vertical mode of buckling and beam lateral mode of buckling of offshore pipelines were investigated. The pipeline was modeled as an elasto-plastic, infinitely long beam with localized imperfection. The seabed was modeled as a fluid-saturated, layered porous medium. The boundary element method, finite element method, and finite difference method were applied for the numerical study. The results show that the buckling behavior of beam vertical mode and beam lateral mode is essentially influenced by the buried depth, initial imperfection, and incline angle. The pipe tends to buckle in the beam lateral mode for the pipe with shallower buried depth, larger imperfection height, and smaller incline angle. The critical buried depth that separates beam vertical mode and beam lateral mode is shallower for smaller excess pore pressure.
Dynamic Response of Tubular T-Joints Under the Influence of
Propagating Cracks
Authors: Nwosu D. I. , Swamidas A. S. J. , Guigne´ J. Y.
Published: February 2008

This paper presents an analytical study on the vibration response of tubular T-joints for detecting the existence of cracks along their intersections. The ABAQUS finite element program was utilized for carrying out the analysis. Frequency response functions were obtained for a joint with and without cracks. The joint was modeled with 8-node degenerate shell elements having 5 degrees of freedom per node. Line spring elements were used to model the crack. The exact crack configuration (semielliptical shape, Fig. 5(b)), as observed from numerous experimental fatigue crack investigations at the critical location, has been achieved through a mapping function, that allows a crack in a planar element to be mapped on to the tube surface. The natural frequency changes with respect to crack depth show little changes, being 4.82 percent for a 83-percent crack depth for the first mode. On the other hand, significant changes have been observed for bending moment and curvature as a function of crack depth. For an 83-percent chord thickness crack, a 97-percent change in bending moment at points around the crack vicinity, and 34.15 to 78 percent change in bending moments, for those locations far away from the crack location, have been observed. Natural frequency change should be combined with other modal parameters such as “bending moment (or bending strain)” and “curvature” changes for crack detection. The presence of the crack can be detected at locations far away from the crack location using such sensors as strain gages.
Extreme Jack-Up Response: Simulation and Nonlinear Analysis
Methods
Authors: Winterstein S. R. , Torhaug R.
Published: February 2008

The nonlinear dynamic response of a jack-up structure under random wave loads is considered. For a simplified jack-up model, average behavior and variability in extreme forces and responses are found from simulation over many 6-h seastates. Weibull and Hermite analytical models of response extremes are also presented and evaluated. These models use shorter, less expensive simulations to estimate a limited number of response statistics, such as moments or parameters of the response peak distribution, and fit analytical models to estimate global extremes. Necessary simulation lengths are established both for direct simulation of extremes, and for analytical extreme models.
The Influence of Alternative Wave Loading and Support Modeling
Assumptions on Jack-Up Rig Response Extremes
Authors: Manuel L. , Cornell C. A.
Published: February 2008

A study is conducted of the response of a jack-up rig to random wave loading. Steady current and wind load effects are also included. The effects of varying the relative motion assumption (in the Morison equation) and of varying the bottom fixity assumptions are investigated. One “fixity” model employs nonlinear soil springs. Time domain simulations are performed using linearized as well as fully nonlinear models for the jack-up rig. Comparisons of response statistics are made for two seastates. Hydrodynamic damping causes the rms response to be lower in the relative Morison case. The absence of this source of damping in the absolute Morison force model gives rise to larger resonance/dynamic effects—this tends to “Gaussianize” the response. Hence, the relative Morison model leads to stronger non-Gaussian behavior than the absolute Morison model. This is reflected in moments as well as extremes. The different support conditions studied are seen to significantly influence extreme response estimates. In general, stiffer models predict smaller rms response estimates, but also exhibit stronger non-Gaussian behavior. The choice of the Morison force modeling assumption (i.e., the relative versus the absolute motion formulation) is seen to have at least a secondary role in influencing response moments and extremes.
Strain Rate Effects on Fracture Toughness of Ship Plate Steels
Authors: Pussegoda L. N. , Malik L. , Bouchard R. , Tyson W. R.
Published: February 2008

Full thickness fracture toughness of conventional ship plate grades, including modern high-strength steels, was determined at loading rates representing quasi-static, intermediate, and impact conditions. For testing at impact strain rates (ε˙ = 5 s−1), customized equipment was designed and developed for a drop tower. It was shown from the CTOD transition temperature curves that the transition temperature increase from quasi-static to intermediate rate (a three-order rate increase) is much greater than the increase from intermediate to impact (a two-order rate increase). Comparison of the dynamic CTOD, CVN, and NDTT indicated that the correlation between the CVN and 0.1-mm dynamic CTOD transition temperature does not hold for the TMCP steels, for which the CVN transition temperature is much lower. By contrast, the results display a very good correlation between the NDTT and 0.1-mm dynamic CTOD transition temperature for all of the steels tested in this program.
The Effect of Nickel on the Mechanical Properties of High-Oxygen Underwater Wet Welds
Authors: Pope A. M. , Teixeira J. C. G. , dos Santos V. R. , Paes M. T. P. , Liu S.
Published: February 2008

The use of oxidizing electrodes for wet welding of offshore structural steels, in spite of their low susceptibility to hydrogen HAZ cracking, is limited, in part, by the poor mechanical properties of their weld deposits. Low levels of carbon, manganese, and other deoxidizers, together with high oxygen contents seems to be one of the reasons for this low performance. This work investigated the influence of nickel additions on the tensile strength and impact resistance of wet welds deposited at 1.1 m of water depth. It was found that welds with nickel contents between 2 and 3 weight percent exhibited maximum toughness and tensile strength. Nickel additions also had a strong effect in reducing the grain size of equiaxed ferrite in the reheated region of underwater wet welds, thereby improving their mechanical properties. The drop of mechanical properties for nickel contents higher than 3 weight percent was associated with weld metal solidification cracking.
Observations of the High-Frequency Range of the Wave Spectrum
Authors: Prevosto M. , Krogstad H. E. , Barstow S. F. , Guedes Soares C.
Published: February 2008

This paper takes a new look at the high-frequency range of the wave spectrum. The analysis is based on data sets from two recent field campaigns offshore Portugal and Crete carried out in the MAST II WAVEMOD project, data from the WADIC experiment in the North Sea, and deep-sea data from Haltenbanken and Vo̸ringplata˚et offshore Norway. In addition, we also show spectra obtained by spectral inversion of ERS-1 SAR imagery. The influence and calibration of wave-measuring instrumentation and the use of wavenumber spectra when comparing spectra from shallow water is emphasized.
The Effect of Springing Response of a TLP on Tether
Fatigue
Authors: Naess A.
Published: February 2008

The purpose of this paper is to investigate the effect on estimated fatigue damage of TLP tethers of the method used to model the springing response. In particular, the goal has been to look into the consequence for long-term fatigue calculation of modeling the springing response as a second-order, sum-frequency process as opposed to assuming that the springing response is Gaussian. It is shown that with a standard engineering approach to the calculation of long-term fatigue damage, this effect is in fact marginal. However, the deviation between the numerical estimates of the quadratic transfer function describing the springing response as provided by different computer codes is found to produce estimates of the long-term fatigue that exhibit substantial variability.
Comparisons of Two Different Mixed Eulerian-Lagrangian Schemes Based
on a Study of Flare-Slamming Hydrodynamics
Authors: Wang M. L. , Troesch A. W. , Maskew B.
Published: February 2008

A comparative study of two different mixed Eulerian-Lagrangian methods is presented. Representative numerical simulations of oscillatory flare-slamming flows are given. Computations based on these two different numerical schemes, i.e., a desingularized method using Rankine ring sources and a source-doublet panel method (e.g., USAERO/FSP©), are compared with experiments. Fourier coefficients of the simulated time histories and experimentally measured forces are given for detailed error comparisons. The numerical simulations demonstrate the ranges of applicability of these two methods. Both are shown to be efficient and robust time-stepping schemes for the fully nonlinear free-surface problem studied here.
Full-Scale Experiments and Analyses of Cellular Hull Sections in
Compression
Authors: Dexter R. J. , Ricles J. M. , Lu L.-W. , Pang A. A.-K. , Beach J. E.
Published: February 2008

Compression tests were conducted on high-strength single-cell and multiple-cell box sections with plate width-to-thickness (b/t) ratios ranging from 48 to 96. Local plate buckling occurred at stresses as low as 5 percent of the yield stress, whereas the ultimate compression stress ranged from 38 to 72 percent of the yield stress. These critical stresses were not significantly affected by the length of the specimen, the number of cells, the boundary conditions, or lateral load. Simple empirical design equations based only on b/t gave estimates of the collapse strength within five percent in all cases. Finite-element analyses were able to predict the significant reserve load-carrying capacity and ductility after ultimate load, which was dependent on the length of the specimen as well as the b/t ratio.
Capacities of Template-Type Platforms in the Gulf of Mexico During
Hurricane Andrew
Authors: Bea R. G. , Loch K. J. , Young P. L.
Published: February 2008

This paper details results from nonlinear analyses of the ultimate limit state performance characteristics of four Gulf of Mexico (GOM) platforms subjected to intense loadings from hurricane Andrew. These four platforms were located to the east of the track of hurricane Andrew, and were thus in the most intense portion of the storm (Smith, 1993). The nonlinear analyses are able to replicate details of the observed behavior of the four structures. This replication is very dependent on realistic characterization of the performance characteristics of the pile foundations and on accurate information on the “as is” condition of the platforms before the storm.
Directional Wave Navigation Radar Measurements Compared With
Pitch-Roll Buoy Data
Authors: A.-Muñoyerro M. Alfonso , Nieto Borge J. C.
Published: February 2008

The knowledge of the spectral behavior of a specific sea region is complete when we know surface elevations and directional wave movements. Usually, sea directional descriptions have been made using pitch-roll buoys, which can provide us with several wave characteristic time series. Alternatively, there are other measure systems, which belong to remote sensing technics, such as shipboard navigation radars. The aim of the present work is to compare results obtained from pitch-roll data and ship radar wave measurements obtained during a campaign in the Cantabric Sea.
Polynomial Approximation of Morison Wave Loading
Authors: Bouyssy V. , Rackwitz R.
Published: February 2008

For offshore structures with slender elements, the modeling of random wave loads by the Morison equation yields an equation of motion which has no analytical solution for response moments except in a few limiting cases. If polynomial approximations of the Morison drag loads are introduced, some procedures are available to obtain the stationary moments of the approximate response. If the response process is fitted by non-Gaussian models such as proposed by Winterstein (1988), the first four statistical moments of the response are necessary. The paper investigates how many terms should be included in the polynomial approximation of the Morison drag loading to accurately estimate the first four response moments. It is shown that a cubic approximation of the drag loading is necessary to accurately predict the response variance for any excitation. For the fit of the first four response moments, at least a fifth-order approximation appears necessary.