bluuebunny/crossref_metadata_2025 huggingface dataset:
Observed and Reported Psychological and Physical Aggression in Young, At‐Risk Couples
Authors: Capaldi Deborah M. , Crosby Lynn
Published: May 2006

The occurrence of observed and reported physical and psychological aggression was examined for young, at‐risk mostly unmarried couples using reports from both partners and observational data. It was predicted that males higher in antisocial behavior would be more likely to have an antisocial partner and that antisocial behavior would predict aggression toward the partner. The prevalence of reported physical aggression was comparable to that found for prior studies and was generally higher for the young women than the young men. Observed aggression was significantly associated with reported aggression, and psychological aggression was associated with physical aggression. Assortative partnering by antisocial behavior was found. The young man's aggression toward his partner was predicted particularly by his antisocial behavior, whereas that of the young woman was predicted by depressive symptoms and low self‐esteem. Relationship satisfaction was associated with the occurrence of psychological aggression but not of physical aggression.
Children's Friends and Behavioral Similarity in Two Social Contexts
Authors: Poulin François , Cillessen Antonius H. N. , Hubbard Julie A. , Coie John D. , Dodge Kenneth A. , Schwartz David
Published: May 2006

The general purpose of this study was to examine similarity between friends with respect to behavior. The specific goals were to consider; 1) different sources of evaluation (peer ratings and direct observations); 2) different social contexts (classroom and play group); and 3) different subtypes of aggressive behavior (proactive and reactive aggression). In the first phase of the study, sociometric assessments and peer evaluations of behavior were conducted in the school setting with third‐grade boys and girls (n ‐ 268). In the second phase, a subsample of boys participated in a series of play group sessions (n = 66). Direct observations and peer ratings of children's behavior were conducted in those sessions. Results showed in both social contexts a tendency towards similarity among friends, especially with respect to aggressive behavior. Separate analyses for subtypes of aggressive behavior revealed that the similarity hypothesis applied for proactive aggression but not for reactive aggression.
Adult Problem Solving: Contributor to Parenting and Child Outcomes in Divorced Families
Authors: Forgatch Marion S. , DeGarmo David S.
Published: May 2006

This cross‐sectional study extends child outcome models by focusing on factors in the adult social domain as contributors to parenting. The sample included 138 divorced mothers, their focal sons, and their support confidants assessed approximately 5 years after marital separation. The multimethod latent variable analysis tested a hypothesized progression stating observed confidant support would enhance problem solving outcomes achieved by mothers and confidants. Resolving parenting and personal issues for the mother was expected to benefit parenting practices (i.e., monitoring, discipline, and mother/child problem solving), which in turn would predict a macro level measure of child antisocial behavior. Analysis of the simplex model supported the progression. The final model explained 36% of the variance in antisocial behavior, 15% of the variance in parenting, and 53% of the variance in problem solving outcome. Dyads with cohabiting partners scored higher on problem solving outcomes than did dyads with friends or family members. The model is discussed in the context of social interactional and social learning theory.
A Critical Examination of Stresses Within and Around Coatings
Authors: Parker Anthony P. , de Swardt Rolf R.
Published: May 2006

In many cases apparently complex interactions between a coating and a substrate may be reduced to a combination of two simple loading scenarios, namely, constant direct stress and linearly varying direct stress applied to the edges of the coating. Stresses within and around coatings are carefully and critically examined. Stress functions incorporating analytical limits are presented for the case of constant and linearly varying direct stress applied to the edge of a coating. Results provide accurate interfacial peeling and shear stresses, and were compared to equivalent finite element (FE) solutions. A technique is proposed for extrapolation of FE results that permits recovery of limiting values. Results were also compared to other recently published data. It is shown that inappropriate use of two sets of results may have produced erroneous interpretations. The particular case of a thin coating prone to craze-cracking is addressed. Direct stress at the free surface of a craze-cracked coating is a strong function of “island” size. In particular, the direct stress at the centerline of such a coating is compressive for island width of <4X coating thickness; this may help to explain the relative dimensions of craze cracking.
Re-Autofrettage
Authors: Jahed Hamid , Moghadam Babak Ahmadi , Shambooli Mojtaba
Published: May 2006

Loading, unloading, and reloading behavior of high-strength steel AISI 4340 (with yield strength of 1080MPa) has been measured using the round bar specimen and method described in (Jahad, H., and Ghanbari, G., 2003, ASME J. Pressure Vessel Technol., 125, pp. 321–325). Tests were conducted at plastic strains up to 3.4% for unloading and reloading. Re-autofrettage is the process of reapplication of overload pressure on an already autofrettaged tube. The question of whether reautofrettage results in a more beneficial compressive stress distribution and, therefore, in extension of life is examined in this study. Because of the profound influence of the Bauschinger effect on the unloading and reloading behavior of high-strength steel, the actual behavior of 4340 steel is used in calculations. It has been shown that with different combinations of first and second overload pressure, higher compressive stress is obtained as compared to a single autofrettage. Using a range of first and second autofrettage pressure, the compressive stress resulted by re-autofrettage is given.
Design Considerations for Electromagnetic Railguns
Authors: Tzeng Jerome , Zielinski Alexander , Schmidt Edward
Published: May 2006

Electromagnetic (EM) railguns are similar to powder guns in that both provide an accelerative force to the projectile, while accepting the resulting recoil impulse. They are designed to contain lateral and axial pressure. They must be capable of surviving the thermal environment to which they are exposed. Although there are similarities, there are also striking differences. Both are explored in the present paper with emphasis placed on EM railgun design.
Effect of Bauschinger Effect and Yield Criterion on Residual Stress Distribution of Autofrettaged Tube
Authors: Huang X. P , Cui W. C.
Published: May 2006

Many analytical and numerical solutions for determining the residual stress distribution in autofrettaged tube have been reported. The significance of the choice of yield criterion, the Bauschinger effect, strain hardening, and the end conditions on the predicted residual stress distribution has been discussed by many authors. There are some different autofrettage models based on different simplified material strain-hardening behaviors, such as a linear strain-hardening model, power strain-hardening model, etc. Those models give more accurate predictions than that of elastic–perfectly plastic model, and each of them suits different strain-hardening materials. In this paper, an autofrettage model considering the material strain-hardening relationship and the Bauschinger effect, based on the actual tensile-compressive stress-strain curve of material, plane-strain, and modified yield criterion, has been proposed. The predicted residual stress distributions of autofrettaged tubes from the present model are compared to the numerical results and the experimental data. The predicted residual stresses are in good agreement with the experimental data and numerical predictions. The effect of Bauschinger effect and yield criterion on residual stress is discussed based on the present model. To predict residual stress distribution accurately, it is necessary to properly model yield criterion, Bauschinger effect, and appropriate end conditions.
The Influence of the Bauschinger Effect on 3D Stress Intensity Factors for Internal Radial Cracks in a Fully or Partially Autofrettaged Gun Barrel
Authors: Perl M. , Levy C. , Rallabhandy V.
Published: May 2006

The influence of the Bauschinger effect (BE) on the three-dimensional, mode I, stress intensity factor (SIF) distributions for arrays of radial, internal, surface cracks emanating from the bore of a fully or partially autofrettaged thick-walled cylinder is investigated. A thorough comparison between the prevailing SIFs for a “realistic” (Bauschinger effect dependent autofrettage (BEDA)) and those for an “ideal” (Bauschinger effect independent autofrettage (BEIA)) is done. The three-dimensional (3D) analysis is performed via the finite element method and the submodeling technique, employing singular elements along the crack front. Both autofrettage residual stress fields, BEDA and BEIA, are simulated using an equivalent temperature field. More than 300 different crack configurations are analyzed. SIFs for numerous crack arrays (n=1-64 cracks), a wide range of crack depth to wall thickness ratios (a∕t=0.01-0.2), various ellipticities (a∕c=0.5-1.5), and different levels of autofrettage (ε=30-100%) are evaluated. The Bauschinger Effect is found to considerably lower the beneficial stress intensity factor due to autofrettage, KIA, by up to 56%, as compared to the case of ideal autofrettage. The reduction in KIA varies along the crack front with a maximum at the point of intersection between the crack plane and the inner surface of the cylinder, decreasing monotonically toward the deepest point of the crack. The detrimental influence of the BE increases as the number of cracks in the array increases and as crack depth decreases. For a partially autofrettaged cylinder, as the level of overstrain becomes smaller the influence of the BE is considerably reduced. As a result, the SIFs due to 100% BEDA differ by <10% as compared to 60% BEDA, and on the average the difference is only about 2–4%.
Gun Barrel Erosion—Comparison of Conventional and LOVA Gun Propellants
Authors: Hordijk A. C. , Leurs O.
Published: May 2006

The research department Energetic Materials within TNO Defence, Security and Safety is involved in the development and (safety and insensitive munitions) testing of conventional (nitro cellulose based) and thermoplastic elastomer (TPE) based gun propellants. Recently our testing capabilities have been extended with vented vessel tests in order to investigate whether or not newly developed (low vulnerability (LOVA)) gun propellants or propellant formulations perform better in erosion tests. At the moment we have two vented vessel tests available, making it possible to determine the extent of erosion from a relatively low loading density to one comparable to a large caliber gun (maximum allowable pressures from 20 to 400MPa). Test pieces of various materials have been used and a number of LOVA and conventional gun propellants have been tested. From the results of these experiments the wear and wear rate have been determined. The erosion dependency on propellant properties like impetus, flame temperature, and combustion gas composition has been determined. Furthermore, an internal ballistics code has been adapted to model the pressure and temperature development in a vented vessel. The results are compared with the experimental results. This model will be described in short and the results presented.
Optimum Autofrettage and Shrink-Fit Combination in Multi-Layer Cylinders
Authors: Jahed Hamid , Farshi Behrooz , Karimi Morvarid
Published: May 2006

The interest in the use of layered cylinders that combine autofrettage and shrink fit in order to extend fatigue lifetimes is increasing. As the number of layers increases, the sequential order of assembly and the size of each layer become more important. To achieve the most benefical result, a design optimization method is required. In this investigation, the optimum design of a three-layered vessel for maximum fatigue life expectancy under the combined effects of autofrettage and shrink fit has been considered. To obtain optimum size of each layer and to optimize the initial stress distribution, the numerical optimization procedure known as the Simplex search method is employed here. The thickness of each layer, shrink-fit pressures, and autofrettage percentages are treated as design variables. Under stress constraints, the operational sequences for assembly of a layered vessel have been formulated in order to lead to optimum results, defined as maximum life expectancy. The fatigue life consideration is based on ASME code provisions and standards for high pressure vessel technology, which define the allowable final crack depth for multilayer vessels. The proposed procedure has been carried out on a number of examples. The results show that, with proper combination of operations significant life enhancement can be achieved using the optimization procedure.
An Experimental-Numerical Determination of the Three-Dimensional Autofrettage Residual Stress Field Incorporating Bauschinger Effects
Authors: Perl M. , Perry J.
Published: May 2006

Autofrettage of large-caliber gun barrels is used to increase the elastic strength of the tube and is based on the permanent expansion of the cylinder bore, using either hydraulic pressure or an oversized swage mandrel. The theoretical solution of the autofrettage problem involves different yield criteria, the Bauschinger effect, and the recalculation of the residual stress field post barrel’s machining. Accurate stress-strain data and their appropriate numerical representations are needed as input for the numerical analysis of the residual stress field due to autofrettage. The purpose of the present work is to develop a three-dimensional (3D) numerical solution for both the hydraulic and the swage autofrettage processes incorporating the Bauschinger effect, using an accurate numerical representation of the experimentally measured material behavior. The new 3D computer code that was developed is capable of determining the stresses, strains, displacements, and forces throughout the entire autofrettage process. The numerical results were validated by an instrumented standard swage autofrettage process. The numerical model was found to excellently reproduce the experimentally measured pushing force as well as the permanent bore enlargement of the barrel. The calculated tangential stresses and the measured ones follow a similar pattern, but their numerical magnitude differs considerably. A wide discrepancy in both pattern and magnitude was found between the calculated and the measured axial stresses. These discrepancies seem to stem from the exact details of the mandrel’s insertion into the tube and are now under further investigation. However, in order to further validate the numerical code an hydraulic autofrettage experiment will be performed, which will hopefully eliminate the swage autofrettage discrepancies.
Dynamical Loading of the Muzzle Area of a Gun Barrel Including a Muzzle Brake
Authors: Bohnsack Eckehard
Published: May 2006

A modern tank gun for light vehicles should be light in weight and have a low recoil force. Therefore it needs an integrated muzzle brake that, however, reduces the strength in the muzzle area. The loading due to gas pressure in this area is as fast as the projectile, and some dynamical effects like traveling waves have to be taken into account. The analytical solution of traveling waves for a smooth tube will be explained on the basis of the shell theory for thin shells. The solution leads to a deeper understanding of the nature of these waves than a pure numerical solution. Since tubes are not really thin, even in the muzzle area, the error that may occur when applying the shell theory is estimated. The analytical solution will be compared to some finite element solutions, which include a multiperforated muzzle brake with a cover tube. The results give some useful hints to the interaction between gas pressure, projectile velocity, and wall thickness and help to reduce the weight of the barrel.
The Influence of the Bauschinger Effect on the Yield Stress, Young’s Modulus, and Poisson’s Ratio of a Gun Barrel Steel
Authors: Perry J. , Perl M. , Shneck R. , Haroush S.
Published: May 2006

The Bauschinger effect (BE) was originally defined as the phenomenon whereby plastic deformation causes a loss of yield strength restraining in the opposite direction. The Bauschinger effect factor (BEF), defined as the ratio of the yield stress on reverse loading to the initial yield stress, is a measure of the magnitude of the BE. The aim of the present work is to quantitatively evaluate the influence of plastic deformation on other material properties such as Young’s modulus and Poisson’s ratio for gun barrel steel, thus extending the definition of the Bauschinger effect. In order to investigate the change in this material’s properties resulting from plastic deformation, several uniaxial tension and compression tests were performed. The yield stress and Young’s modulus were found to be strongly affected by plastic strain, while Poisson’s ratio was not affected at all. An additional result of these tests is an exact zero offset yield point definition enabling a simple evaluation of the BEF. A simple, triphase test sufficient to characterize the entire elastoplastic behavior is suggested. The obtained experimental information is readily useful for autofrettage residual stress field calculations.
Characterization and Comparison of Magnetron Sputtered and Electroplated Gun Bore Coatings
Authors: Mulligan Christopher P. , Smith Stephen B. , Vigilante Gregory N.
Published: May 2006

The demands to increase range, rate of fire, and muzzle velocity have resulted in increased wear and erosion problems in gun tubes. To increase the service life of gun tubes, a number of bore-coating systems are being considered for replacement of the current electroplated high-contractile chromium coating. Two such coating systems are cylindrical magnetron sputtered (CMS) Cr coatings and CMS Ta∕Cr bilayer coatings. Cylindrical magnetron sputtering is a high-rate vacuum deposition process that has been applied to 120mm tubes. Characterization studies of the electroplated and CMS coatings were completed to determine the applicability of these coating/substrate systems for gun bore protection. Each coating system is subjected to a series of tests, including adhesion, microhardness, compositional analysis, and vented erosion-simulation testing (VES). VES testing is completed via a laboratory combustion chamber that reproduces the transient thermal and chemical environments of tank cannon firing on small chord sections of 120mm coated gun tubes. In addition to the aforementioned characterization tests, metallography, scanning electron microscopy, and energy dispersive spectroscopy are conducted on each specimen before and after VES testing to evaluate the thermal stability of the coating and the severity of the thermal damage imposed. The mechanisms of damage are investigated, including void formation and micropit growth, oxidation and erosion, and thermomechanical cracking. In addition, methods to further increase resistance to thermal damage are discussed to increase the service life of future gun tube systems.
A Comparison of Methods for Predicting Residual Stresses in Strain-Hardening, Autofrettaged Thick Cylinders, Including the Bauschinger Effect
Authors: Gibson Michael C. , Hameed Amer , Parker Anthony P. , Hetherington John G.
Published: May 2006

High-pressure vessels, such as gun barrels, are autofrettaged in order to increase their operating pressure and fatigue life. Autofrettage causes plastic expansion of the inner section of the cylinder, setting up residual compressive stresses at the bore after relaxation. Subsequent application of pressure has to overcome these compressive stresses before tensile stresses can be developed, thereby increasing its fatigue lifetime and safe working pressure. This paper presents the results from a series of finite element models that have been developed to predict the magnitude of these stresses for a range of end conditions: plane stress and several plane-strain states (open and closed ended, plus true plane strain). The material model is currently bilinear and allows consideration of strain hardening and the Bauschinger effect. Results are compared to an alternative numerical model and a recent analytical model (developed by Huang), and show close agreement. This demonstrates that general purpose finite element analysis software may be used to simulate high-pressure vessels, justifying further refining of the models.
Projectile Driving Band Interactions With Gun Barrels
Authors: Andrews Tony D.
Published: May 2006

This paper discusses results from a series of trials carried out to determine the effect of the projectile driving band on the stress applied to a 155mm gun barrel during firing. The interference between the driving band and gun barrel can apply significant loads to the barrel and, in extreme cases, lead to premature cracking and failure of the barrel. Strain gage data from firing trials has been used to characterize the external strain from firing different projectiles and charges to identify potential problems and provide information for fatigue analysis. Very high band strains were routinely measured under “oiled bore” conditions, i.e., after barrel cleaning and also during the first one to three rounds of a serial following a long pause in firing, such as at the start of a day’s firing. In general, the strain associated with the driving band was seen to decrease with increased charge zone, barrel wear, and, at higher charge zones, distance along the barrel. In the majority of tests fired at maximum charge, there was no strain peak associated with the driving band in the forward part of the barrel. In conjunction with these experimental observations, a laboratory study has been carried out on the effect of a narrow pressure band on the deformation of a thick-walled tube. An apparatus was constructed in order to pressurize a known length of a smooth-bore cylinder. Sealing width at the edges of the band was minimized to reduce edge effects, and an oversize pressurized “cap” was used to ensure that the bandwidth remained constant during the experiments. Spacer disks were used to vary the bandwidth and also to adjust the cylinder position relative to the band. Measured external strains on the tubes were compared to calculations based on analytical solutions for step pressure changes and are shown to be in good agreement.
Material Models for the Finite Element Analysis of Materials Exhibiting a Pronounced Bauschinger Effect
Authors: de Swardt Rolf R.
Published: May 2006

Realistic material models have been developed on the basis of the experimental investigation of reverse loading with actual Bauschinger effect and implemented into a two-dimensional finite element computer program. The developed program is capable of treating the elastoplastic deformation behavior of thick-walled cylinders during both loading and unloading phases. Strain hardening may occur during loading, and reverse yielding may occur during unloading at a yield strength significantly reduced due to the Bauschinger effect. Three different models for the reverse hardening are presented. Strain hardening during reverse yielding may have a different slope than for forward loading, and it may also be nonlinear. The intended application is for autofrettage analysis of thick-walled cylinders. Being a numerical solution, it will also be very useful for finite element analysis of residual stress experimental procedures and also in the determination of more accurate stress intensity factors for autofrettaged cylinders that had undergone reverse yielding due to the Bauschinger effect.
Stress Analysis of Autofrettaged Midwall Cooled Compound Gun Tubes
Authors: de Swardt Rolf R. , Andrews Tony D.
Published: May 2006

Analytical solutions for shrink-fit compound gun tubes were used to study the effects of the liner/sleeve interface diameter, the radial interference, and the effect of machining tolerances on tube strength. Finite element analyses were then done of a midwall cooled compound gun tube where a loose-fitting inner tube (liner) is permanently deformed by means of hydraulic pressure to lock it to the outer tube (sleeve). The interaction between the liner and sleeve was modeled with contact elements. The effect of machining subsequent to the hydraulic autofrettage was taken into account. Simulations were first done for smooth tubes with initial clearance of varying magnitude and, second, for the case where the liner has axial semi-circular cooling channels machined on its outer surface. Manufacturing tolerances were found to be much less critical for the hydraulic autofrettage than with the shrink-fit option. The interface diameter seems to be a relatively insensitive parameter. Relatively large initial clearance between inner and outer tubes can be tolerated. The hydraulic autofrettage option therefore seems better than the shrink-fit only option for compound gun tubes. It was demonstrated that the effect of the cooling channels on the stresses in the tube is significant and substantially weakens the inner tube. However, it is still possible to produce a workable design.
Thermomechanically Controlled Erosion in Army Cannons: A Review
Authors: Underwood John H. , Vigilante Gregory N. , Mulligan Christopher P. , Todaro Mark E.
Published: May 2006

Metallographic characterization is presented of thermal damage of Cr-coated steel in a fired cannon; Cr and Ta coated steel in a vented-erosion-simulator; and bulk Si3N4 in laser heating. Common features of rapid crack-induced erosion are noted. (i) Cracks form normal to the surface, often permanently open, indicating tensile stress was present at some point during thermal damage. (ii) Softening of Cr and Ta coatings and Si3N4 occurs near the heated surface, verified by metallography and hot hardness. The transformation of steel beneath the coatings is used as an in-situ verification of temperatures that cause thermal damage. (iii) Crack-induced under-cutting of thermal-damage islands is observed for coatings and bulk Si3N4. A thermomechanical analysis of rapid crack-induced erosion observed in severe cannon firing and firing simulation suggests the following key failure mechanisms common to metals and Si3N4. (i) High near-bore transient temperatures increase thermal expansion compression and concurrently decrease the elevated temperature strength. For metals, the thermal compression stress greatly exceeds strength, to depths of about 0.5mm. (ii) Thermal stress exceeding strength produces compressive yielding, which, upon cooling, causes tensile residual stress and cracking. The near-bore residual tension is high enough to cause one-cycle cracking of both Cr and Ta coatings; hydrogen from combustion enters via the cracks and causes cracking in the steel below the coating. For Si3N4, cracks are encouraged by the low fracture toughness of Si3N4. (iii) Repeated thermal cycles deepen and widen cracks to form islands that can be undercut, leading to island removal and rapid erosion failure of the cannon. For Cr and Ta coatings, undercutting is by hydrogen cracking in the steel and degradation of the coating interface by combustion products that enter via the cracks. For Si3N4, undercutting is by direct thermomechanical cracking.
Hydraulic Testing of Ordnance Components
Authors: Andrews Tony D. , Brine Fred E.
Published: May 2006

This paper describes a range of hydraulic fatigue and pressure tests carried out on gun barrels and ordnance components in support of weapons research and development programs. Cyclic testing of representative sections of large caliber guns has been routinely carried out to determine safe fatigue life for operational use. Ultrasonic techniques have been developed for mapping multiple cracks within the gun barrels by which periodic examinations of barrels during testing have been used to build up histories of crack initiation and growth. In relatively unworn barrels multiple cracks, initiated along each rifling groove, are shown to form in an extremely stable array that can grow to several millimeters depth, in agreement with calculated stress intensity factors, before one crack accelerates to dominate final failure. The development of localized erosion from extensive firing is shown to significantly affect the subsequent hydraulic fatigue cycling by generation of only one or two cracks as well as the prior removal of heavily prestressed bore material. Tests on fume extractor sections of barrels show that cracking initiates in the jet holes and only grows to the bore at late stages. Introduction of different levels of autofrettage acts to bias the radial location of the cracks. An extensive experimental program of work has been carried out in support of design studies on mid-wall cooled gun barrels exploring a number of different configurations for construction of compound tubes and the results of numerical simulations of the assembly process have been compared with strain gauge measurements during the experimental procedure on scale tubes. Subsequent hydraulic cycling was used to determine the fatigue implications of the processing route.
A Method for Fatigue Analysis of Piping Systems on Topsides of FPSO Structures
Authors: Spanos P. D. , Sofi A. , Wang J. , Peng B.
Published: May 2006

Pipelines located on the decks of FPSO systems are exposed to damage due to sea wave induced random loading. In this context, a methodology for estimating the fatigue life of fluid-conveying pipelines is presented. The pipeline is subjected to a random support motion that simulates the effect of the FPSO heaving. The equation of motion of the pipeline is derived by assuming small amplitude displacements, modeling the empty pipeline as a Bernoulli-Euler beam, and adopting the so-called “plug-flow” approximation for the fluid (Fluid-Structure Interactions Slender Structures and Axial Flow, Academic Press, San Diego, Vol. 1). Random vibration analysis is carried out by the Galerkin method selecting as basis functions the natural modes of a beam with the same boundary conditions as the pipeline. The discretized equations of motion are used in conjunction with linear random vibration theory to compute the stress spectrum for a generic section of the pipeline. For this purpose, the power spectrum of the acceleration at the deck level is determined by using the Response Amplitude Operator of the FPSO hull. Finally, the computed stress spectrum is used to estimate the pipeline fatigue life employing an appropriate S-N fatigue curve of the material. An illustrative example concerning a pipeline simply supported at both ends is included in the paper.
Probabilistic Analysis of Characteristic Pressure for LNG Tanks
Authors: Graczyk Mateusz , Moan Torgeir , Rognebakke Olav
Published: May 2006

Background. New challenges in LNG shipping, such as ship size growth, trading routes with more severe weather conditions, need for operating with unrestricted filling level and new propulsion systems attract very much attention in marine and offshore oriented community. One of the main concerns is the prediction of loads caused by violent fluid motion in cargo tanks. In the paper we address the problem of determining characteristic extreme values of sloshing pressures for structural design. This involves estimating ship motion in a long-term period, fluid motion in the tank, excited pressures, and relevant structural responses. Method of Approach. Ship motion analysis is based on linear strip theory. In order to investigate the dependence of the sloshing response on sea conditions, an approach based on statistical characteristics of the tank motion is utilized as well as a multimodal approach for fluid motion in a tank. However, an appropriate theoretical/numerical approach, which can be used for a realistic prediction of the most extreme pressure has not yet been developed. Thus, experiments are utilized for the most severe sea states for a chosen tank filling level. Results. Our main contribution in the paper includes the statistical analysis of experimental short term pressure distribution. The choice and fit of probability distribution models is addressed, with due account of different physical mechanisms causing impacts. The models are evaluated. The most critical tank areas for sloshing loads are briefly discussed. Appropriate dynamic response of the tank structure needs to be investigated by accounting for temporal and spatial distribution of sloshing loads. These two factors are also addressed in the paper. The variability of results obtained by processing data from multiple test runs is discussed. Conclusions. The three-parameter Weibull and generalized Pareto statistical models are fitted to the data and evaluated. They prove to accurately describe sloshing excited pressures. However, the highest data points are underestimated by the both distributions. Generalized Pareto model results in more conservative estimates. The threshold level of peaks used in a fit of generalized Pareto distribution was investigated. Based on this, it is set to a level of a 0.85–0.87 quantile of peak values. The big influence of spatial and temporal distribution on the estimates is reported. Uncertainty in measured pressures originating from inherent fluid motion variability exceeds the uncertainty resulting form ship motions' variability. Moreover, generalized Pareto model results in higher variability.
Characterizing the Wave Environment in the Fatigue Analysis of Flexible Risers
Authors: Sheehan John M. , Grealish Frank W. , Harte Annette M. , Smith Russell J.
Published: May 2006

As the offshore industry moves towards deeper water developments and continues to embrace harsh environments, unbonded flexible pipes are increasingly being utilized as a cost effective riser solution. Furthermore, with the advent of issues such as nonpristine annuli environments, the fatigue performance of these flexible risers is becoming a critical issue. This paper presents an overview of the comparisons between deterministic and stochastic global fatigue analysis techniques. Methods used to perform both deterministic and stochastic analyses are outlined, from performing the global analyses to using local models to generate armor wire stresses and subsequent fatigue damage. The paper identifies the key issues in the analysis performed and presents key results and conclusions with regard to the characterization of the wave environment in the global fatigue analysis of flexible risers.
Second Order Wave Diffraction Around a Fixed Ship-Shaped Body in Unidirectional Steep Waves
Authors: Zang J. , Gibson R. , Taylor P. H. , Eatock Taylor R. , Swan C.
Published: May 2006

The objective of this research, part of the EU FP5 REBASDO Program, is to examine the effects of second order wave diffraction in wave run-up around the bow of a vessel (FPSO) in random seas. In this work, the nonlinear wave scattering problem is solved by employing a quadratic boundary element method. A computer program, DIFFRACT, has been developed and recently extended to deal with unidirectional and directional bichromatic input wave systems, calculating second order wave diffraction loads and free surface elevation under regular waves and focused wave groups. The second order wave interaction with a vessel in a unidirectional focused wave group is presented in this paper. Comparison of numerical results and experimental measurements conducted at Imperial College shows excellent agreement. The second order free surface components at the bow of the ship are very significant, and cannot be neglected if one requires accurate prediction of the wave-structure interaction; otherwise a major underestimation of the wave impact on the structure could occur.
Buckling/Elastoplastic Collapse Behavior and Strength of Continuous Tee-Bar Stiffened Plates
Authors: Mukherjee Kenneth Sunil , Yao Tetsuya
Published: May 2006

The influence of residual stress distributions should be properly taken into account in the structural analysis of stiffened plates. The generally assumed residual stress distributions in the analyses often have constant values across their cross sections. This approximation is also applied to identical stiffeners that are constructed by different methods, such as rolled and built-up tee-bar stiffened plates. This paper focuses on buckling/plastic collapse behavior of rolled and built-up tee-bar stiffened plates with experimentally determined residual stress distributions in their cross sections. The structural behavior until collapse of these two types of tee-bar stiffeners is analyzed in detail, using residual stresses measured from experimental results. Various numerical modelling aspects of stiffened plated structures are briefly discussed and finally the influence of differences in residual stress distributions on buckling/plastic collapse behavior of continuous stiffened plates is studied based on selected results, using the Finite Element Method.
Response Analysis of a Truss-Pontoon Semisubmersible With Heave-Plates
Authors: Srinivasan Nagan , Chakrabarti Subrata , Radha R.
Published: May 2006

An offshore platform that is efficiently designed to reduce the wave excitation forces and increase the separated-flow damping could qualify as a platform operating even near its resonance. Such design could make this concept cost-effective, as well as operationally more productive with minimum downtime. The principal purpose of this paper is to describe an offshore platform design that could face the resonance efficiently. The paper applies the concept of both hydrodynamic added mass and separated-flow damping intelligently in the design of a large deepwater floating vessel on column-stabilized principle. The platform is designed to face resonance due to extreme waves and utilizes the damping to control its motion, thereby qualifying its field application. The design is justified and verified with the results of a scaled-model study in a large wave tank. The results of the correlation of theoretical study with the model test results are presented herein. A few variations of the deepwater platform concept are discussed.
Detailed Analysis of the Wake of a DP Thruster Emphasizing Comparison Between LDV and SPIV Techniques
Authors: El Lababidy S. , Bose N. , Liu P. , Di Felice F.
Published: May 2006

To provide experimental data on the hydrodynamic characteristics and features of dynamic positioning (DP) thrusters under variable operating conditions, wake measurements were performed on a DP thruster model using 2D laser Doppler velocimetry (LDV) and stereoscopic particle image velocimetry (SPIV). These tests were performed with and without a nozzle and over a range of advance coefficient values including the bollard pull condition. In this paper, a detailed analysis of the hydrodynamic characteristics of the wake at a plane equal to a distance of 0.5 diameters downstream from the thruster, at advance coefficient values of 0, 0.4, and 0.45 are presented for both the LDV and SPIV measurements showing a comparison between the results of each technique. The effect of the duct and of changes in the advance coefficient values is presented in this paper.
Fatigue Capacity of FPSO Structures
Authors: Bergan Pål G. , Lotsberg Inge
Published: May 2006

This paper presents an overview of a joint industry project, addressing the problem of fatigue capacity of FPSOs (FPSO=ship shaped structures used for floating production storage and offshore loading). Spectral methods are becoming standard methodology for fatigue assessments of FPSOs. This methodology is well suited to numerical methods in combination with finite element representation of the global structure and structural details for response analyses. A proper link between calculated stress and fatigue capacity is required in order to achieve a reliable design. The project has generated significant amounts of numerical data as well as laboratory fatigue test data of typical ship details to improve the design basis for this. An overview of this project together with some links to the main results and recommendations from this project will be presented in this paper.
Time-course of the human medial olivocochlear reflex
Authors: Backus Bradford C. , Guinan John J.
Published: May 2006

The time-course of the human medial olivocochlear reflex (MOCR) was measured via its suppression of stimulus-frequency otoacoustic emissions (SFOAEs) in nine ears. MOCR effects were elicited by contralateral, ipsilateral or bilateral wideband acoustic stimulation. As a first approximation, MOCR effects increased like a saturating exponential with a time constant of 277±62ms, and decayed exponentially with a time constant of 159±54ms. However, in ears with the highest signal-to-noise ratios (4∕9), onset time constants could be separated into “fast,” τ=∼70ms, “medium,” τ=∼330ms, and “slow,” τ=∼25s components, and there was an overshoot in the decay like an under-damped sinusoid. Both the buildup and decay could be modeled as a second order differential equation and the differences between the buildup and decay could be accounted for by decreasing one coefficient by a factor of 2. The reflex onset and offset delays were both ∼25ms. Although changing elicitor level over a 20dB SPL range produced a consistent systematic change in response amplitude, the time course did not show a consistent dependence on elictor level, nor did the time-courses of ipsilaterally, contralaterally, and bilaterally activated MOCR responses differ significantly. Given the MOCR’s time-course, it is best suited to operate on acoustic changes that persist for 100’s of milliseconds.
Comparing the rhythm and melody of speech and music: The case of British English and French
Authors: Patel Aniruddh D. , Iversen John R. , Rosenberg Jason C.
Published: May 2006

For over half a century, musicologists and linguists have suggested that the prosody of a culture’s native language is reflected in the rhythms and melodies of its instrumental music. Testing this idea requires quantitative methods for comparing musical and spoken rhythm and melody. This study applies such methods to the speech and music of England and France. The results reveal that music reflects patterns of durational contrast between successive vowels in spoken sentences, as well as patterns of pitch interval variability in speech. The methods presented here are suitable for studying speech-music relations in a broad range of cultures.
Comparison of in-air evoked potential and underwater behavioral hearing thresholds in four bottlenose dolphins (
Tursiops truncatus
)
Authors: Finneran James J. , Houser Dorian S.
Published: May 2006

Traditional behavioral techniques for hearing assessment in marine mammals are limited by the time and access required to train subjects. Electrophysiological methods, where passive electrodes are used to measure auditory evoked potentials (AEPs), are attractive alternatives to behavioral techniques; however, there have been few attempts to compare AEP and behavioral results for the same subject. In this study, behavioral and AEP hearing thresholds were compared in four bottlenose dolphins. AEP thresholds were measured in-air using a piezoelectric sound projector embedded in a suction cup to deliver amplitude modulated tones to the dolphin through the lower jaw. Evoked potentials were recorded noninvasively using surface electrodes. Adaptive procedures allowed AEP hearing thresholds to be estimated from 10to150kHz in a single ear in about 45min. Behavioral thresholds were measured in a quiet pool and in San Diego Bay. AEP and behavioral threshold estimates agreed closely as to the upper cutoff frequency beyond which thresholds increased sharply. AEP thresholds were strongly correlated with pool behavioral thresholds across the range of hearing; differences between AEP and pool behavioral thresholds increased with threshold magnitude and ranged from 0to+18dB.
Time-dependent stochastic inversion in acoustic travel-time tomography of the atmosphere
Authors: Vecherin Sergey N. , Ostashev Vladimir E. , Goedecke George H. , Wilson D. Keith , Voronovich Alexander G.
Published: May 2006

Stochastic inversion is a well known technique for the solution of inverse problems in tomography. It employs the idea that the propagation medium may be represented as random with a known spatial covariance function. In this paper, a generalization of the stochastic inverse for acoustic travel-time tomography of the atmosphere is developed. The atmospheric inhomogeneities are considered to be random, not only in space but also in time. This allows one to incorporate tomographic data (travel times) obtained at different times to estimate the state of the propagation medium at any given time, by using spatial-temporal covariance functions of atmospheric turbulence. This increases the amount of data without increasing the number of sources and∕or receivers. A numerical simulation for two-dimensional travel-time acoustic tomography of the atmosphere is performed in which travel times between sources to receivers are calculated, given the temperature and wind velocity fields. These travel times are used as data for reconstructing the original fields using both the ordinary stochastic inversion and the proposed time-dependent stochastic inversion algorithms. The time-dependent stochastic inversion produces a good match to the specified temperature and wind velocity fields, with average errors about half those of the ordinary stochastic inverse.
Acoustical origin of rainbands in an ideal tropical hurricane
Authors: Elder S. A.
Published: May 2006

An acoustical model of hurricane rainband formation is proposed. Self-excited acoustic resonance inside the spinning eye produces strong azimuthal and radial standing waves. These modes can cause large temperature fluctuations about the dew point which are believed to be responsible for observed dry/wet bands in the outer storm disk. Distortion of standing wavefronts into spirals occurs in the transition layer region between approximately geostrophic flow inside the eyewall and irrotational flow outside. Tonal emissions from hurricane eyes should be detectable at great distances and are likely to be in a range below 0.01Hz.
Piezoelectric vibration control by synchronized switching on adaptive voltage sources: Towards wideband semi-active damping
Authors: Badel A. , Sebald G. , Guyomar D. , Lallart M. , Lefeuvre E. , Richard C. , Qiu J.
Published: May 2006

Synchronized switch damping (SSD) principle and derived techniques have been developed to address the problem of structural damping. Compared with standard passive piezoelectric damping, these new semi-passive techniques offer the advantage of self-adaptation with environmental variations. Unlike active damping systems, their implementation does not require any sophisticated signal processing nor any bulky power amplifier. This paper presents an enhancement of the SSD technique on voltage source (SSDV) which is the most effective of the SSD techniques. The former SSDV technique uses a constant continuous voltage sources whereas the proposed enhancement uses an adaptive continuous voltage source which permits fitting the mechanical braking force resulting from the SSDV process to the vibration level. A theoretical analysis of the SSDV techniques is proposed. Experimental results for structural damping under single frequency and for vibration control of a smart board under white noise excitation are presented and confirm the interest of the enhanced SSDV compared to other SSD techniques. Depending on the excitation type, a 4- to 10-dB damping gain can be achieved.