Showing papers by "Naval Surface Warfare Center published in 2001"

Effect of quenching on the magnetostriction on Fe/sub 1-x/Ga/sub x/ (0.13x<0.21)

Abstract: The magnetostriction (/spl lambda//sub 100/) of b.c.c. Fe is increased over 10-fold at room temperature by the substitution of /spl sim/20% gallium for Fe. Fe/sub 1-x/Ga/sub x/ alloys with x between 0.19 and 0.214 that are quenched from 800/spl deg/C exhibit magnetostrictions /spl sim/25% higher than those furnace-cooled at 10/spl deg//min. We propose that this great increase of magnetostriction above that of Fe in Fe-Ga alloys is not due to conventional magnetoelastic effects but due to the substitutive presence of asymmetrically shaped clusters of the Ga atoms. As the concentration of solute atoms approaches 25%, the lattice becomes relaxed with formation of a more ordered structure and the magnetostriction decreases in value.

Five techniques for increasing the speed and accuracy of PIV interrogation

Abstract: This paper explores several methods for increasing the efficiency and accuracy of particle image velocimetry (PIV) data analysis. The time to directly compute the correlation function to determine the displacement in PIV interrogation windows is reduced using two techniques. First, a scheme that calculates the correlation for 16 pixels in parallel is implemented. A further increase in efficiency results from using a truncated multiplication scheme that calculates 82% of the answer while reducing the work by 84%. Second, advantage is taken of the common practice of overlapping adjacent interrogation windows by not recorrelating the portion of the new window that overlaps the old. For the commonly used 50% overlap, the speed of vector calculation can theoretically be increased 300%. In practice, the improvement depends on the implementation of the method. The most efficient algorithm doubles the processing speed at 50% overlap. Accuracy is increased using three methods. First, a technique for enhancing PIV images to increase the contrast between the particles and the background is presented. This method is particularly useful when experimental exigencies result in low contrast images. Second, a method is presented for resolving the velocity in areas of high velocity gradient where the correlation map contains multiple peaks. Third, equalizing the histogram of sub-pixel adjustments should eliminate peak locking. Sample data show a `decrease' in error of 15%.

Thermomechanical response of AL-6XN stainless steel over a wide range of strain rates and temperatures

Abstract: To understand and model the thermomechanical response of AL-6XN stainless steel, uniaxial compression tests are performed on cylindrical samples, using an Instron servohydraulic testing machine and UCSD's enhanced Hopkinson technique. True strains exceeding 40% are achieved in these tests, over the range of strain rates from 0.001/s to about 8000/s, and at initial temperatures from 77 to 1000 K. In an effort to understand the underlying deformation mechanisms, some interrupted tests involving temperature and low- and high-strain rates, are also performed. The microstructure of the undeformed and deformed samples is observed by optical microscopy. The experimental results show: (1) AL-6XN stainless steel displays good ductility (strain >40%) at low temperatures and high-strain rates, with its ductility increasing with temperature; (2) at high-strain rates and 77 K initial temperature, adiabatic shearbands develop at strains exceeding about 40%, and the sample breaks, while at low-strain rates and 77 K, axial microcracks develop at strains close to 50% or greater; (3) dynamic strain aging occurs at temperatures between 500 and 1000 K and at a strain rate of 0.001/s, with the peak value of the stress occurring at about 800 K, and becoming more pronounced with increasing strain and less pronounced with increasing strain rate; and (4) the microstructure of this material evolves with temperature, but is not very sensitive to the changes in the strain rate. Finally, based on the mechanism of dislocation motion, paralleled with a systematic experimental investigation, a physically based model is developed for the deformation behavior of this material, including the effect of viscous drag on the motion of dislocations, but excluding the dynamic strain aging effects. The model predictions are compared with the results of the experiments. Good agreement between the theoretical predictions and experimental results is obtained. In order to verify the model independently of the experiments used in the modeling, additional compression tests at a strain rate of 8000/s and various initial temperatures, are performed, and the results are compared with the model predictions. Good correlation is observed.

Structural characterisation of the highly deintercalatedLixNi1.02O2 phases (with x ≤ 0.30)

Abstract: The full structural characterisation of the highly deintercalated LixNi1.02O2 (x ≤ 0.30) phases has been performed. The structure of the Li0.30Ni1.02O2 phase was refined by the Rietveld method. The cationic distribution was found to be identical to that of the pristine material. A study of the Li//LixNi1.02O2 system at high potential has shown the successive formation of two phases with O3 (AB CA BC) and O1 (AB) oxygen packing, respectively, near the NiO2 composition. Since slab gliding is at the origin of the O3 to O1 transition, layer displacement faults were observed in these two phases. For the O3 phase, as soon as all the lithium ions are removed from an interslab space, an O1-type fault occurs locally. In contrast, for the O1 phase, the presence of extra-nickel ions in the interslab space prevents slab gliding in the vicinity and, therefore, O3-type interslab spaces remain in the O1-type packing. The X-ray diffraction patterns were simulated using the DIFFaX program. It was shown that the stabilisation of the O1-type packing at the very end of the deintercalation process is due to a minimisation of the interactions between the p orbitals of the oxygen ions through the van der Waals gap. A two-phase domain is observed between Li0.30NiO2 and a composition close to NiO2 since, for very low lithium contents, the Ni3+/Ni4+ ordering (and the lithium/vacancy ordering) is no longer possible and the difference in size between the cations leads to the formation of constraints which destabilise the Ni3+ ions in a lattice where Ni4+ ions prevail. At the end of the deintercalation process, the NiO2 compound appears to be highly covalent, therefore, the steric effects prevail over the electrostatic repulsion effects, as in chalcogenides.

High grain size stability of nanocrystalline Al prepared by mechanical attrition

Abstract: Grain growth in nanocrystalline (nc) Al with a grain size of 26 nm produced by cryogenic mechanical milling was studied through x-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. Grain growth kinetics resembled those of ball-milled nc Fe. For homologous temperatures (T/TM) of 0.51–0.83, the time exponent n from D1/n − D01/n = kt was 0.04–0.28, tending toward 0.5 as T/TM increased. Two grain-growth regimes were distinguished: below T/TM = 0.78 growth ceased at an approximate grain size of 50 nm while at higher temperatures, grain growth proceeded steadily to the submicrometer range. Grain growth over the range of temperatures studied cannot be explained in terms of a single thermally activated rate process. The observed high grain size stability was attributed primarily to impurity pinning drag associated with the grain growth process.

An overview of SAX99: acoustic measurements

Abstract: A high-frequency acoustic experiment was performed at a site 2 km from shore on the Florida Panhandle near Fort Walton Beach in water of 18-19 m depth. The goal of the experiment was, for high-frequency acoustic fields (mostly In the 10-300-kHz range), to quantify backscattering from the seafloor sediment, penetration into the sediment, and propagation within the sediment. In addition, spheres and other objects were used to gather data on acoustic detection of buried objects. The high-frequency acoustic interaction with the medium sand sediment was investigated at grazing angles both above and below the critical angle of about 30/spl deg/. Detailed characterizations of the upper seafloor physical properties were made to aid in quantifying the acoustic interaction with the seafloor. Biological processes within the seabed and the water column were also investigated with the goal of understanding their impact on acoustic properties. This paper summarizes the topics that motivated the experiment, outlines the scope of the measurements done, and presents preliminary acoustics results.

Algorithm fusion for automated sea mine detection and classification

Abstract: The fusion of multiple detection/classification algorithms is proving a very powerful approach for dramatically reducing false alarm rate, while still maintaining a high probability of detection and classification. This has been demonstrated in several Navy sea tests. The high-resolution sonar is one of the principal sensors used by the Navy to detect and classify sea mines in mine hunting operations. For such sonar systems, substantial effort has been devoted to the development of automated detection and classification (D/C) algorithms. These have been spurred by several factors including (1) aids for operators to reduce work overload, (2) more optimal use of all available data, and (3) the introduction of unmanned mine hunting systems. The environments where sea mines are typically laid (harbor areas, shipping lanes, and the littorals) give rise to many false alarms caused by natural, biologic, and man-made clutter. The objective of the automated D/C algorithms is to eliminate most of these false alarms while still maintaining a very high probability of mine detection and classification (PdPc). The benefits of fusing the outputs of multiple D/C algorithms have been studied. We refer to this as algorithm fusion. The results have been remarkable, including reliable robustness to new environments. Even though our experience has been gained in the area of sea mine detection and classification, the principles described herein are general and can be applied to fusion of any D/C problem (e.g., automated medical diagnosis or automatic target recognition for ballistic missile defense).

Grain growth behavior of a nanostructured 5083 Al–Mg alloy

Abstract: A nanostructured 5083 Al–Mg alloy powder was subjected to various thermal heat treatments in an attempt to understand the fundamental mechanisms of recovery, recrystallization and grain growth as they apply to nanostructured materials A low-temperature stress relaxation process associated with reordering of the grain boundaries was found to occur at 158 °C A bimodal restructuring of the grains occurred at 307 °C for the unconstrained grains and 381 °C for the constrained grains An approximate activation energy of 56 kJ/mol was found for the metastable nanostructured grains, while an approximate activation energy of 142 kJ/mol was found above the restructuring temperature

Structure of Pt/Ru Catalysts Using X-ray Absorption Near Edge Structure Studies

Abstract: Pt/Ru catalysts with two very different structures were examined with X-ray absorption near edge structure (XANES). One sample was an industrial methanol fuel cell Pt/Ru alloy catalyst black, and the second was a carbon-supported Pt/Ru catalyst. In both cases the as-prepared Pt/Ru catalysts were found, with XANES, to be predominately in the form of Pt and Ru oxides. When these catalysts were placed in an electrochemical cell and held in the potential region where methanol oxidation occurs, XANES data indicate that the metal oxides were reduced to the metallic form. These results also demonstrate that conclusions about the electrocatalytic activity of Pt/Ru materials for methanol oxidation drawn from the characterization of as-prepared samples have little relevance.

A Prognostic Modeling Approach for Predicting Recurring Maintenance for Shipboard Propulsion Systems

Abstract: Accurate prognostic models and associated algorithms that are capable of predicting future component failure rates or performance degradation rates for shipboard propulsion systems are critical for optimizing the timing of recurring maintenance actions As part of the Naval maintenance philosophy on Condition Based Maintenance (CBM), prognostic algorithms are being developed for gas turbine applications that utilize state-of-the-art probabilistic modeling and analysis technologies Naval Surface Warfare Center, Carderock Division (NSWCCD) Code 9334 has continued interest in investigating methods for implementing CBM algorithms to modify gas turbine preventative maintenance in such areas as internal crank wash, fuel nozzles and lube oil filter replacement This paper will discuss a prognostic modeling approach developed for the LM2500 and Allison 501-K17 gas turbines based on the combination of probabilistic analysis and fouling test results obtained from NSWCCD in Philadelphia In this application, the prognostic module is used to assess and predict compressor performance degradation rates due to salt deposit ingestion From this information, the optimum time for on-line waterwashing or crank washing from a cost/benefit standpoint is determinedCopyright © 2001 by ASME

Diffraction radiation diagnostics for moderate to high energy charged particle beams

Abstract: Diffraction radiation (DR) is produced when a charged particle passes through an aperture or near a discontinuity in the media in which it is traveling. DR is closely related to transition radiation (TR), which is produced when a charged particle traverses the boundary between media with different dielectric constants. In contrast to TR, which is now extensively used for beam diagnostic purposes, the potential of DR as a non-interceptive, multi-parameter beam diagnostic remains largely undeveloped. For diagnostic measurements it is useful to observe backward reflected DR from a circular aperture or slit inclined with respect to the beam velocity. However, up to now, well-founded equations for the spectral-angular intensities of backward DR from such apertures have not been available. We present a new derivation of the spectral-angular intensity of backward DR produced from an inclined slit for two orientations of the slit axis, i.e., perpendicular and parallel to the plane of incidence. Our mathematical approach is generally applicable to any geometry and simpler than the Wiener Hopf method previously used to calculate DR from single edges. Our results for the slit are applied to the measurement of orthogonal beam size and divergence components. We discuss the problem of separating the simultaneous effects of these beam parameters on the angular distribution of DR and provide solutions to this difficulty. These include use of the horizontal and vertical polarization components of the radiation from a single slit and interferences from two inclined slits. Examples of DR diagnostics for a 500 MeV beam are presented and the current limitations of the technique are discussed.

Temperature, strain rate, stress state and the failure of HY-100 steel

Abstract: The influence of temperature and strain rate on the deformation and failure behavior of HY-100 steel has been examined as a function of stress state using notched and un-notched axisymmetric tensile specimens. Behavior over the range of temperatures/strain rates from −85°C and 1 s −1 to 27°C and 10 −3 s −1 shows an equivalence of decreasing test temperature or increasing strain rate on deformation behavior in a manner that can be predicted by the thermally activated flow theory. Over the entire range of temperatures/strain rates, the influence of stress state on failure is such that two void coalescence mechanisms control failure; at low stress triaxialities, relatively equiaxed voids grow to impingement, while at high triaxialities, a void-sheet process intervenes linking elongated MnS-initiated voids by a shear instability. The failure strains decrease rapidly with increasing stress triaxiality ratio in a similar manner for all temperatures and strain rates except for an intermediate stress triaxiality condition where the void-sheet mode of failure extends to lower stress triaxialities under cryogenic test conditions.

The effects of high-dose gamma irradiation on high-voltage 4H-SiC Schottky diodes and the SiC-SiO/sub 2/ interface

Abstract: The effects of radiation on high-voltage 4H-SiC Schottky diodes for use in extreme environment power supplies are investigated for the first time. Diodes were fabricated with a wide range of barrier heights (1.06-1.60 eV) and were evaluated after being exposed to a /sup 60/Co gamma radiation source. DC current-voltage characteristics were measured after several radiation doses, with no observable degradation in the diode forward or reverse characteristics up to a total dose of 4 Mrad(Si). Measured breakdown voltages of post-irradiated diodes increase approximately 200 V compared to the virgin devices and are attributed to increased negative interface charge, as determined by MOS capacitor measurements and correlated with numerical breakdown simulations.

Microwave Nondestructive Detection of Corrosion Under Thin Paint and Primer in Aluminum Panels

Abstract: Detection of corrosion, under paint and primer, in various metallic structural components, particularly when used in moist and salty environments is an important practical concern. Moreover, nondestructive testing techniques that do not require paint removal are desired. Near-field microwave nondestructive inspection techniques, employing open-ended rectangular waveguide probes, have shown tremendous potential for detecting and evaluating the presence of corrosion under paint in steel substrates. The objective of this investigation has been to investigate the potential of these techniques for detecting corrosion under paint and primer in aluminum substrates. To accomplish this goal, an electromagnetic formulation, simulating detection of corrosion in layered structure using open-ended rectangular waveguide probes, was used to gain an insight into the functionality of measurement parameters such as the frequency of operation and standoff distance. In conjunction with this simulation, the dielectric properties of paint, primer, real and chemically produced aluminum oxide were measured in a wide range of microwave frequencies (2.6–18 GHz). The results showed that the dielectric properties of paint, primer and aluminum oxide are very similar to each other. Subsequently, the theoretical simulation was conducted in a wide frequency band (8.2–40 GHz). The overall result of the simulation effort was that higher frequencies and standoff distances of a few mm are more optimal for detecting thin corrosion layers under paint. Two specially prepared aluminum panels with induced areas of corrosion and surface pitting were produced as well. Using these panels and several phase sensitive measurement systems, experiments were conducted producing 2-D images of various areas of these panels. Images were produced at different standoff distances and at frequencies of 9, 11.725, 24.1, and 33.5 GHz. The overall results of the experimental investigation were extremely promising when detecting the thin regions of corrosion in these panels. This paper presents the approach and results of this investigation.

Ion storage dosimetry

Abstract: The availability of a reliable, accurate and cost-effective real-time personnel dosimetry system is fascinating to radiation workers. Electronic dosimeters are contemplated to meet this demand of active dosimetry. The development of direct ion storage (DIS) dosimeters, a member of the electronic dosimeter family, for personnel dosimetry is also an attempt in this direction. DIS dosimeter is a hybrid of the well-established technology of ion chambers and the latest advances in data storage using metal oxide semiconductor field effect transistor (MOSFET) analog memory device. This dosimeter is capable of monitoring legal occupational radiation doses of gamma, X-rays, beta and neutron radiation. Similar to an ion chamber, the performance of the dosimeter for a particular application can be optimized through the selection of appropriate wall materials. The use of the floating gate of a MOSFET as one of the electrodes of the ion chamber allows the miniaturization of the device to the size of a dosimetry badge and avoids the use of power supplies during dose accumulation. The concept of the device, underlying physics and the design of the DIS dosimeter are discussed. The results of preliminary testing of the device are also provided.

Inferring propeller inflow and radiation from near-field response, Part 2 : Empirical application

Abstract: Data analysis techniques were previously developed for rotating machinery that predicted the far-field radiation, inferred inflow characteristics, and defined the near-field/far-field acoustic Green's function based on measurements of the pressure near field (Minniti, R. J., Blake, W. K., and Mueller, T. J., Inferring Propeller Inflow and Radiation from Near-Field Response, Part 1: Analytic Development, AIAA Journal, Vol. 39, No. 6, 2000, pp. 1030-1036). The techniques are applied to a free-running propeller in subsonic flow. As a first case, the propeller ingesting large-scale, mean-flow distortions as would be present downstream of stators or inlet guide vanes was considered. This simplified case allowed qualitative analysis in the time domain and complimenting quantitative analysis in the frequency domain. In addition, the case acted as a calibrating configuration to map the frequency response of the individual blades to the incoming flow by varying the number of distortions present and the rotational speed of the propeller. Based on the results of the first case, the analysis was extended to the propeller ingesting grid-generated turbulence. Because of the complex nature of the flow, all analysis was completed in the frequency domain. By the use of the techniques in Inferring Propeller Inflow and Radiation from Near-Field Response, Part 1: Analytic Development, an estimate of the blade summation gain was used to complete the direct solution of the aeroacoustic problem and predict the acoustic far field from a measurement of the ingested flow. Additionally, the inflow character was inferred from the near-field measurements.

Mitigation of platform generated magnetic noise impressed on a magnetic sensor mounted in an autonomous underwater vehicle

Abstract: The detection and localization of targets of interest in the very shallow water areas and especially in the surf zone are much more difficult problems than in the deep ocean. To overcome these problems, it is necessary to augment existing fleet sensor capability with additional technology. Furthermore in keeping with Navy policy, it is desirable to remove the diver from harms way. A potential solution is to utilize a small autonomous underwater vehicle (AUV) instrumented with both a buried target sonar and the real time tracking gradiometer (RTG). This paper describes the procedures required to successfully place a magnetic gradient sensor array on an AUV. The first step was to magnetically characterize the AUV. This was accomplished by passing the AUV by a stationary RTG and then by externally mounting that RTG at several locations on the AUV which was then placed in simulated at-sea motion on a nonmagnetic three-axis motion table. Analysis of the data revealed that the favored location of a magnetic sensor is near the nose of the vessel and that the initial degradation, in this location, caused by the presence of the powered AUV was 30 dB above sensor noise. The degradation was caused primarily by the vehicle's electrical systems. Initial measurements also revealed the presence of several ferromagnetic components that should be replaced with nonmagnetic equivalents when practical. A detailed plan of magnetic noise mitigation is also presented. It involves several steps for implementation, including the substitution of nonferrous components for ferrous, maximizing the separation between the sensor and magnetic field sources, minimizing current loops and using auxiliary current and magnetic field sensors capable of generating noise-canceling signals.

Weibull stress model for cleavage fracture under high‐rate loading

Abstract: This paper examines the effects of loading rate on the Weibull stress model for prediction of cleavage fracture in a low-strength, A515-70 pressure vessel steel. Interest focuses on low-to-moderate loading rates (K I < 2500 MPa√m s -1 ). Shallow cracked SE(B) specimens were tested at four different loading rates for comparison with previous quasi-static tests on shallow notch SE(B)s and standard C(T)s. To utilize these dynamic experimental data, we assume that the Weibull modulus (m) previously calibrated using quasi-static data remains invariant over the loading rates of interest. The effects of dynamic loading on the Weibull stress model enter through the rate-sensitive material flow properties, the scale parameter (σ u ) and the threshold Weibull stress (σ w-min ). Rate-sensitive flow properties are modelled using a viscoplastic constitutive model with uniaxial, tension stress-plastic strain curves specified at varying plastic strain rates. The analyses examine dependencies of σ w-min and σ u on K I . Present results indicate that σ w-min and σ u are weak functions of loading rate K I for this pressure vessel steel. However, the predicted cumulative probability for cleavage exhibits a strong sensitivity to σ u and, consequently, the dependency of σ u on K I is sufficient to preclude use of the static σ u value for high loading rates.

Inferring propeller inflow and radiation from near-field response, Part 1 : Analytic development

Abstract: In general, the physics of the relationship between the pressure field surrounding a rotating propeller in subsonic flow and the flow characteristics is understood. However, quantification of this relationship in a way that allows engineering analysis of propeller noise is limited by complete definition of the inflow distortions. Therefore, a way of inferring this relationship and the distortion characteristics unobtrusively and in situ has been developed. The technique is based on the assumption that measurements of the unsteady pressure on the blades are available. From the pressures, the technique predicts the radiated acoustic far field, infers incoming flow characteristics, and defines Green's function between the near and far pressure fields. The analysis combines theoretical and empirical treatments of pressure data to infer the acoustic quantities. Thus, the turbulence ingestion problem is approached in a practical manner without the need for many of the simplifying assumptions required by purely theoretical means. The technique is developed for use on experimental data. The technique is subsequently applied to a propeller operating downstream of large-scale, mean-flow distortions, and ingesting broadband turbulence (Minniti, R. J., Blake, W. K., and Mueller, T. J., Inferring Propeller Inflow and Radiation from Near-Field Response, Part 2: Empirical Application, AIAA Journal, Vol. 39, No. 6, 2001, pp. 1037-1046).

Electromagnetic scattering from large steady breaking waves

Abstract: A submerged hydrofoil generated large steady breaking waves of 0.3 m and 0.4 m height in a circulating water channel. We measured water fraction in the breakers with conductivity probes. We observed the radar cross-section of the breakers at X-band with a pulsed step-frequency instrumentation radar with high spatial resolution in the downstream direction. The normalized radar cross-section increases with increasing elevation angle of observation for both vertical and horizontal polarization. This variation is consistent with a simple interpretation of the breaking wave as a diffuse (Lambertian) surface. However, the observed sizes and shapes of fluid elements in the breakers clearly show that construction of a theory for electromagnetic scattering from first principles will be challenging. We also obtained the velocity spectrum of the scattering features within the breakers. This spectrum indicates that slower moving small liquid elements rather than the faster moving large disturbances are responsible for most of the electromagnetic scattering.

Nature's algorithms [genetic algorithms]

Abstract: Combinatorial optimization problems typically require every possible solution to be evaluated to ensure finding the optimal solution. Since such exhaustive searches are often impractical, there is now a vast body of heuristic algorithms for them. Among the algorithms are those based on metaphors borrowed from other areas of science. The idea is that key elements of physical processes can be used abstractly to form the basis of an optimization algorithm. This article presents a broad overview of several metaphor-based algorithms, including the widely-used genetic and simulated annealing algorithms.