Outer Hull Research Articles

Fatigue Prediction Verification of Fiberglass Hulls

The growing use of marine composite materials has led to many technical challenges and one is predicting lifetime durability. This analysis step has a large uncertainty due to the lack of data from in-service composite vessels. Analytical models based on classical lamination theory, finite-element analysis, ship motions, probability and wind and wave mechanicswere used in this project to predict hull laminate strains, and fatigue tests were used to determine S-N residual stiffness properties of coupons. These predictions and test data were compared against two cored fiberglass sisterships having significantly different fatigue histories and undamaged laminates representing a new vessel. Strains were measured while underway and good correlation was achieved between predictions and measurements. Fatigue damage indicators were identified which could be used in vessel inspection procedures. Endurance limits were found to be near 25% of static failure load, indicating that a fatigue design factor of four is required for infinite service with this material. Standard moisture experiments using boiling water were compared with long-term exposure. Results indicated the boiling water test yielded significantly conservative values and was not a reliable means of predicting long-term effects. Panel tests were compared with a combined coupon and finite-element procedure. Results indicated the proposed procedure was a viable substitute, at least for the materials studied. A rational explanation for using thicker outer skin laminates in marine composites was identified through single-sided moisture flex tests. These showed that the reduced strength and stiffness due to moisture of the outer hull skin laminate could be compensated by increased thickness. Although the resulting unbalanced laminate is not ideal from a warping standpoint, the approach leads to consistent tensile failure of the inner skin when subjected to normal loads. Permeability considerations make this desirable for hull laminates.

The Southern Traffic Lane Spill (T/V Command): A Case Study of Spiller Accountability1

ABSTRACT On September 24, 1998, the T/V Command had a small spill in San Francisco Bay, California while taking on bunkers in Anchorage Nine. The cause was determined to be due to a small crack in the outer hull plating of the tank. The T/V Command departed on the evening of September 26 after completing temporary repairs required by the Captain of the Port (COTP)/Federal On-Scene Coordinator (FOSC). The next morning, a large 10-mile by 2-mile oil slick was discovered just south of the entrance to San Francisco Bay. This triggered one of the largest, most far-reaching oil spill investigations ever. Since no one took responsibility for this spill, the U.S. Coast Guard accessed the Oil Spill Liability Trust Fund (OSLTF) and established a Unified Command with the state of California Department of Fish and Game, Office of Spill Prevention and Response (OSPR) to begin immediate cleanup. The Coast Guard and OSPR also began an aggressive joint investigation to track down the spiller. Hundreds of vessels had entered or departed San Francisco Bay during the 5-day window before the spill was discovered. The investigators were able to narrow the search and sample vessels. The Coast Guard Marine Safety Lab (MSL) and OSPR's lab were able to match the spilled oil to the T/V Command,. The Coast Guard tracked down the location of the T/V Command and began the first ever request for high seas boarding of a vessel for an environmental crime. A Coast Guard team from the USCGC Boutwell boarded the T/V Command 200 miles off Guatemala to begin the investigation. A follow-on multiagency team of investigators, led by the Coast Guard again, boarded the vessel in Panama. In a plea bargain agreement, the T/V Command's operator, master, and chief engineer pled guilty in federal court to criminal charges stemming from the spill on September 27, 1998, remarkably 1 year from the date of the original spill. The operator agreed to pay over $9.4 million dollars in criminal and civil penalties. This paper and presentation discusses the complexities of this international spill response investigation and events leading up to the settlement.

Adaptive cone-kernel time-frequency analysis

Presents a technique to adaptively optimize the performance of the cone-kernel distribution (CKD) by varying the cone length in response to changing signal properties. The result is an adaptive CKD that preserves the outer hull of signal time support, yields excellent results on real signals, outperforms fixed-length CKDs, and requires only slightly more computation than a fixed-kernel distribution.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Finite Element Analysis of the Quarter Scale Advanced Double Hull Design

ABSTRACT The design of advanced unidirectionally stiffened double hull surface ships is motivated by economic, military, civilian and environmental concerns. Major concerns include economical producibility. reduced signature, enhanced survivability and damage resistance to grounding. Verification of structural analysis capabilities, identification of collapse mechanisms and evaluation of structural integrity are issues that need to be addressed.Congress established the Advanced Double Hull Technology Project following the Oil Pollution Act of 1990, and provided FY 92 and FY 93 funding to investigate double hull technology for naval surface ships and commercial application of ecologically sound bulk fuel carriers. As part of this project the Office of Naval Research (ONR) tasked the Carderock Division of the Naval Surface Warfare Center (CD/NSWC) to evaluate the crash‐worthiness of the double hull concept in stranding incidents. This work included a series of quarter‐scale stranding experiments conducted at the National Institute of Standards and Technology (NIST). Finite element analysis was performed to demonstrate the accuracy of non‐linear, large deflection numerical modeling by comparison with the experimental results.The Advanced Double Hull (ADH) design features longitudinal web stiffe‐ners with an inner‐outer hull spacing of 79 inches. In this investigation, a quarter scale model of a representative section of the hull with an inner‐outer hull spacing of 18.5 inches was used to analyze stranding. The structural performance and load transfer mechanisms of the ADH quarter scale model during a simulated stranding event were the primary objectives of the analysis. In the stranding event, an object on the bottom of a harbor or shallow waterway was simulated by a spherically tipped conical penetrator. The penetrator initially contacted the outer hull. A 30 inch displacement of the penetrator was applied beyond the initial point of contact.Explicit finite element methods were utilized to determine the structural response and collapse mechanisms produced by the stranding event. Large strain elastic‐plastic constitutive response and geometric non‐linearity were accounted for in the finite element analysis. The progressive penetration leads to outer hull rupture, longitudinal web deformation, contact between the outer hull and the webs, contact between the outer and inner hull and deformation of the inner hull. The inner hull deformed 11.5 inches inward during the finite element analysis and was deflected without fracture to a predicted maximum load of 1.060,040 lbs. The levels of deformation, fracture and plastic energy dissipation of the analysis model compared favorably with the experimental results. Detailed examination of the finite element results provided an understanding of the structural elastic‐plastic performance associated with stranding and a validated methodology for further use by designers and analysts.

Pyrolysis and combustion of corncobs in a fluidized bed: Measurement and analysis of behavior

A study of corncob combustion in a fluid bed, for investigation of kinetic behavior, provided reproducible data on the variation of mass, volume, and density with time that was interpreted quantitatively using boundary layer diffusion (BLD) theory, and qualitatively using heat transfer and pyrolysis kinetics. The core of a corncob is an inner cylinder of pith surrounded by two annular cylinders: an inner cob, of about 80% of the total weight, and an outer hull. A total of 120 corncob segments, roughly of length equal to their diameter, and each about 13 g were used. They were immersed in a fluid sand bed at 650°C for periods up to 160 s, using a cage to withdraw the particles after immersion. The cobs were initially cylindrical but they became spherical during reaction so that combustion theory for spheres could be used in the analysis. In the first 10 s, about 10% of the corncob mass burned off, as loss of a fraction of the outer (lower density) hull, and with an increase in mean density by about 20%. In the next 80 s, as heat penetrated into the cob, there was, simultaneously: pyrolysis of the cob, governed jointly by the rate of heat penetration and the pyrolysis kinetics; and reduction of volume by combustion of the hull, quantitatively predicted by BLD theory. The char residue after pyrolysis was about 20% of the original mass, and was spherical, of low density. Its rate of combustion was also quantitatively described by BLD combustion theory. These results showed that the behavior of corncobs in combustion was reproducible, predictable, and amenable to mathematical analysis that could be applied to model descriptions of fluid bed combustion of these materials.

二重船殻構造モデルタンクよりの油流出

Cargo behaviors of the double hull tankers after the groundings and collisions which result in the damages of both the outer hull plating and the inner hull plating were investigated using the 1/50 scale models representing a midship section of a typical cargo tank of VLCC. Tests were carried out in still water, and a lubricating oil was used as the test fluid. Oil outflows were measured under the various conditions for the double bottom heights and the double side widths, the tank sizes, the extents and the positions of the rupture, the axial offsets of the ruptures, the initial thickness of the water layer in the double hull space, the drafts and the cargo levels. The dynamic characteristics of the water and cargo flow in the double hull space after an opening of the rupture were investigated.

Elaborate hull cupules of chiton eggs focus the sperm: A Scanning Electron Microscope study

The outer hull of most chiton (Mollusca: Polyplacophora) eggs is elaborated into complex spines or cupules that project, from the surface effectively increasing egg diameter. Cupules are either open or closed in free-spawning species but are reduced to flat plates in brooding forms. In open cupule species such as Mopaliaciliata (Fig. 1) invariably sperm swim inside the cupules and become segregated into one of seven internal channels. This was first demonstrated by rolling eggs on sticky tape to remove cupules prior to sputter coating (Fig. 2). Sperm penetrate the thin hull at the base of each cupule during the first stage of fertilization (Figs.3, 4) . One can slice the egg in half using a Keisei microknife (Japan) and examine sperm penetration at the cut surface (Fig. 3).

Effects of junctions on radiation by plate and shell modes into a surrounding fluid.

This discussion considers methods for computing radiation into surrounding water due to vibrating sources within a submerged vessel with internal structures. The vessel is viewed as a collection of plates and shells; the vibration of each component can be written as a superposition of flexural, extensional, and shear motions. Depending on the wave velocity, there can be two components to the radiated field. For example, the extensional wave can radiate continuously into water as it propagates along the outer hull. The angle of radiation is sin−1(vw/vl), where vl and vw are the velocities of the extensional mode and the acoustic wave in water, respectively. In addition, there will be radiation over a 180° spectrum of angles that originates from the vicinity of junctions between the hull and internal structures such as ribs and bulkhead. This radiation is an end effect arising from the fact that the shell/plate waves have a finite starting point. (Note that the flexural mode can also radiate through this diffraction mechanism even when the frequency is below the coincidence frequency.) An important aspect of this paper will be to evaluate the relative importance of these two mechanisms for various shell/plate modes. [Work supported by ONR.]

Invasion percolation on substrates with correlated disorder

Simulations have been carried out to investigate invasion percolation with trapping on two dimensional substrates with a multifractal distribution of bond threshold probabilities. Suprisingly, the spatial correlations in the bond thresholds appear not to influence or influence only slightly the fractal scaling properties. Fractal dimensionalities, D, of about 1.82 for the entire clusters, about 1.45–1.5 for the hull and about 1.4–1.45 for the outer hull were obtained for all bond invasion percolation models with and without spatial correlations. The exponent τ describing the power law distribution of trapped defender cluster sizes has a value of about 1.90 (( D + d)/ d where d is the Euclidean dimensionality). The value for D of 1.4–1.45 for the outer hull is regarded as being consistent with but not in good agreement with the theoretical value of 4 3 for ordinary percolation. The value of about 1.50 obtained for the total hull is much different from the value of 1.75 associated with ordinary percolation hulls. The difference between the value of 1.82 obtained from the entire cluster and the theoretical percolation value of vl is (1.895833) is also regarded as being significant. The simulation results also show that the fractal dimensionality for the total hull is much different for bond and site invasion percolation with trapping on substrates with uncorrelated disorder while the outer hulls have the same fractal dimensionality for both models. For the site invasion percolation model D hull ⋍ 7 4 while for the bond invasion percolation model D hull ⋍D outer hull .

Noise damping system for torpedoes or the like

A noise damping system incorporating in the hull of an underwater torpedo or the like which includes a power plant having a boiler. An inner hull section includes hotwell passages about the boiler whereby subcooled liquid in the hotwell passages absorbs heat from the boiler. A noise damping elastomer layer is provided about the inner hull section whereby the hotwell passages insulate the noise damping layer from the boiler. An outer hull section has condenser passages about the noise damping layer. The hotwell passages and the condenser passages are part of the closed circulation system of the power plant.

Limit Analysis and Design of a Semi-Submerged Concrete Hull for an Ocean Thermal Differences Power Plant

Utilizing the concepts of limit analysis, and ultimate strength of concrete, a design approach for large diameter immersed reinforced concrete cylindrical hulls has been developed. The method is applied to the design of a semi-submerged ocean thermal differences power plant. For the structure under consideration which consists of an outer and inner hull, separate operating and maintenance conditions were assumed for design. Equilibrium equations, and an iteration method to determine plastic moments, axial forces and shears corresponding to a collapse condition have been developed. Computer results for the outer and inner hull are tabulated for the two loading conditions based on design thickness of 3 ft. For a given thickness, details of reinforcing are given, and an admissible interaction diagram for moment and axial load to satisfy the various loading conditions is presented.

A Study on the Hull Girder Strength of Container Ships with Large Hatch Openings

This paper presents the investigated resuts of numerical simulation pertaining to the hull girder strength of container ships in irregular sea.Using the so-called total system of hull girder strength analysis developed by the authors, the analysis of the long-term prediction of structural response of three container ships is carried out.And the wave-induced stresses in longitudinal strength members, distortion of hatch openings and the torsional deformation of hull girder are studied from the point of view of the long-term prediction.As a result of this simulation, the following conclusions are obtained.(1) In the middle part of ship, the wave-induced normal stress in the upper deck at the side edge of hatch opening is in the stress range of 89.5kg/mm2 and the wave-induced shearing stress in the outer hull at the load water line is below 10kg/mm2 with probability level 10-6.The normal stress of outer hull at the bilge part is in the same level with that of the upper deck.(2) In the fore hold structure, the normal stress of the upper deck is almost in the same level with that of the middle part of ship.Furthermore the torsional deformation of hull girder is considerably large compared with that of the middle part of hull because of the decrease in the torsional rigidities.(3) As to the distortion of hatch openings, the elongation Δl of the diagonal length of them is largest in the hatch of the middle part, but there are small differences in the ratio Δl/l with same probability level.

Weight Considerations for Deep Submersibles

Conventional shallow submersible vehicles depend on the pressure hull for buoyancy, but deep submersibles depend on some type of bulk material for buoyancy. As a consequence, the design of very deep submersibles requires new considerations on the vehicle weight. The purpose of this paper is to evaluate the many parameters which affect the boat weight to see which ones are most influential on total weight. To accomplish this objective, a simplified mathematical expression is derived which describes the total weight for a deep submergence vehicle. The expression contains both structural and nonstructural weight items. The structural items include the pressure capsule, outer hull, foundations, and hard tanks. The nonstructural items are the equipment, buoyancy material, and payload. Each weight item is then examined in detail to determine what parameters affect the boat weight. The results show that the greatest weight reduction is possible with the equipment. This is because the state-of-the-art equipment used for deep submersibles has a weight almost equal to three times its displacement, and to furnish sufficient buoyancy material in the boat to float such equipment results in a large weight penalty.

Micromorphology of conidiospores of Aspergillus niger by electron microscopy.

ABSTRACTThe fine structure of conidiospores of Aspergillus niger has been studied by means of ultrathin sectioning and electron microscopy. Permanganate fixation of the conidia preserved the details of their inner structural components and enhanced the general contrast within the sections. The conidiospores are characerized by their peculiar surface structures composed of three distinct components; an outer hull, a spore coat or wall, and an intermediate space. As a consequence of the swelling of the conidia, both the outer hull and the intermediate space almost completely disappear, and a variety of the intracytoplasmic organelles becomes visible in large numbers. The mature conidia at the resting stage appear to possess a more electron‐dense cytoplasm than that of the parent hyphae of the organism. They also contain a nucleus and a few mitochondria within the cytoplasm. The significance of these structures and their relationship to the parent hyphal cells are discussed.

MODERN MARINE PAINTS

The conditions to which marine paints are subjected are undoubtedly very much more severe than those which any similar types of paint meet on land. Conditions of application, which are more often than not bad, add further complications. In dry‐dock painting the ship must undock to schedule and painting must, therefore, go on regardless of rain, frost and fog. As a result, most marine paints and compositions for the outer hull must be a compromise between the ideal and the practical, rather than the best possible material which could be used under perfectly controlled conditions.

The equilibrium moisture content of tung fruit and its components at different relative humidities

SummaryThe equilibrium moisture contents at 25°C. were determined for the whole tung fruit, the outer hull, the inner hull, shell, kernels, and seed of the fruit, and on the cake from continuous screw presses at nine different relative humidities. The relative humidities were maintained by enclosing saturated solutions of different salts in desiccators in a room maintained at constant temperature.

Furfural from corncobs : II—The Bureau of Chemistry experimental plant and process for furfural production

A study of corncob combustion in a fluid bed, for investigation of kinetic behavior, provided reproducible data on the variation of mass, volume, and density with time that was interpreted quantitatively using boundary layer diffusion (BLD) theory, and qualitatively using heat transfer and pyrolysis kinetics. The core of a corncob is an inner cylinder of pith surrounded by two annular cylinders: an inner cob, of about 80% of the total weight, and an outer hull. A total of 120 corncob segments, roughly of length equal to their diameter, and each about 13 g were used. They were immersed in a fluid sand bed at 650°C for periods up to 160 s, using a cage to withdraw the particles after immersion. The cobs were initially cylindrical but they became spherical during reaction so that combustion theory for spheres could be used in the analysis. In the first 10 s, about 10% of the corncob mass burned off, as loss of a fraction of the outer (lower density) hull, and with an increase in mean density by about 20%. In the next 80 s, as heat penetrated into the cob, there was, simultaneously: pyrolysis of the cob, governed jointly by the rate of heat penetration and the pyrolysis kinetics; and reduction of volume by combustion of the hull, quantitatively predicted by BLD theory. The char residue after pyrolysis was about 20% of the original mass, and was spherical, of low density. Its rate of combustion was also quantitatively described by BLD combustion theory. These results showed that the behavior of corncobs in combustion was reproducible, predictable, and amenable to mathematical analysis that could be applied to model descriptions of fluid bed combustion of these materials.