Showing papers by "Naval Surface Warfare Center published in 2000"

Magnetostrictive properties of body-centered cubic Fe-Ga and Fe-Ga-Al alloys

Abstract: The magnetic and magnetostrictive properties of Fe/sub 1-x/Ga/sub x/ and Fe/sub 1-x-y/Ga/sub x/Al/sub y/ (a+y<0.3) single crystals were measured under compressive stresses up to 120 MPa and in magnetic fields up to 1 kOe. Values of /spl lambda//sub 100/ exceeding 200 ppm were observed in samples of Fe/sub 83/Ga/sub 17/ from 180 K to room temperature. Only a small monotonic decrease in magnetostriction with temperature was found. On the other hand, /spl lambda//sub 111/ maintained small negative values close to those of b.c.c. Fe. In all cases, no higher order magnetostrictive terms were detectable. With 15 to 20 atomic percent replacement of Fe by Ga, the magnetizations remain high (M, /spl cong/1.8 T) and the magnetic anisotropies reduced (K/sub 1//spl cong/10/sup 4/ J/m/sup 3/). Values of the 'stiff' (high magnetic field) Young's modulus, Bulk modulus, Poison's ratio, and elastic constant C/sub 11/-C/sub 12/ for Fe/sub 85/Ga/sub 15/ at room temperature are, respectively, 77 GPa, 111 GPa, 0.38, and 56 GPa.

Radiated noise characteristics of a modern cargo ship

Abstract: Extensive measurements were made of the radiated noise of M/V OVERSEAS HARRIETTE, a bulk cargo ship (length 173 m, displacement 25 515 tons) powered by a direct-drive low-speed diesel engine—a design representative of many modern merchant ships. The radiated noise data show high-level tonal frequencies from the ship’s service diesel generator, main engine firing rate, and blade rate harmonics due to propeller cavitation. Radiated noise directionality measurements indicate that the radiation is generally dipole in form at lower frequencies, as expected. There are some departures from this pattern that may indicate hull interactions. Blade rate source level (174 dB re 1 μPa/m at 9 Hz, 16 knots) agrees reasonably well with a model of fundamental blade rate radiation previously reported by Gray and Greeley, but agreement for blade rate harmonics is not as good. Noise from merchant ships elevates the natural ambient by 20–30 dB in many areas; the effects of this noise on the biological environment have not been widely investigated.

Synthesis of nanostructured WC-12 pct Co coating using mechanical milling and high velocity oxygen fuel thermal spraying

Abstract: A nanostructured WC-12 pct Co coating was synthesized using mechanical milling and high velocity oxygen fuel (HVOF) thermal spraying. The variation of powder characteristics with milling time and the performance of the coatings were investigated using scanning electron microscope (SEM), X-ray, transmission electron microscope (TEM), thermogravimetric analyzer (TGA), and microhardness measurements. There is no evidence that indicates the presence of an amorphous phase in the sintered WC-12 pct Co powder, and the binder phase in this powder is still crystalline Co. Mechanical milling of up to 20 hours did not lead to the formation of an amorphous phase in the sintered WC-12 pct Co powder. During the initial stages of the milling, the brittle carbide particles were first fractured into fragments and then embedded into the binder phase. This process gradually formed polycrystal nanocomposite powders of the Co binder phase and W carbide particles. The conventional cold welding and fracturing processes primarily occurred among the Co binder powders and polycrystal composite powders. The nanostructured WC-12 pct Co coatings, synthesized in the present study, consist of an amorphous matrix and carbides with an average particle diameter of 35 nm. The coating possesses an average microhardness of 1135 HV and higher resistance to indentation fracture than that of its conventional counterpart.

The mechanical threshold stress constitutive-strength model description of HY-100 steel

Abstract: A generalized three-term mechanical threshold stress (MTS) strength model description, considering athermal, thermal, and strain-hardening contributions to flow stress, is employed to characterize the constitutive stress-strain response of HY-100 steel. Aspects of the MTS framework pertinent to United States Navy HY steels are discussed, and a calibration methodology is presented for determining MTS strength model parameters. In addition, a linear strain-hardening modification to the existing structure-evolution expression (flow-stress saturation) is proposed to better describe the large-strain strain-hardening behavior. Polycrystalline plasticity calculations suggest that the linear-like hardening behavior is a consequence of deformation-path-dependent texture evolution. Calculation results are applied to MTS model stress-strain predictions and, in part, help explain the differences between compression and torsion test data.

Control of human atrial fibrillation

Abstract: Chaos control has been applied to control atrial fibrillation in humans. Results are presented on the application and evaluation of chaos control for slowing and regularizing local electrical activation of the right atrium of humans during induced atrial fibrillation.

Biofouling and barnacle adhesion data for fouling‐release coatings subjected to static immersion at seven marine sites

Abstract: Little is known about the performance of fouling‐release coatings at different geographical locations. An investigation was designed to measure the differences in biofouling and biofouling adhesion strength on three known silicone formulations and an epoxy control at seven static immersion sites located in California, Florida, Hawaii, Hong Kong, India, Italy and Singapore. The study found that whilst the relative performance of the coatings was similar at each site, there were statistically significant differences in the type and intensity of fouling that developed on the coatings and in barnacle adhesion strength among sites. The results emphasize the importance of evaluating potential coatings at more than one static immersion site.

In Situ X‐Ray Absorption Spectroscopy Study of Li ( 1 − z ) Ni ( 1 + z ) O 2 ( z ≤ 0.02 ) Cathode Material

Abstract: In situ X‐ray absorption spectroscopy study of phases shows that the Ni K edge continuously shifts to higher energies with a decrease in Li content in a manner consistent with oxidation of Ni(III) to Ni(IV) The Ni K‐edge energy for is consistent with that observed for chemically prepared quadrivalent Ni in . Variations in the coordination numbers, bond lengths, and disorders as a function of state of charge (i.e., the value of x) are consistent with the following facts: (i) a Jahn‐Teller distortion for Ni(III), (ii) an undistorted environment for Ni(IV), and (iii) an electrochemical oxidation of Ni(III) to Ni(IV). © 2000 The Electrochemical Society. All rights reserved.

Planning for verification, validation, and accreditation of modeling and simulation applications

Abstract: A comprehensive and detailed verification, validation and accreditation (VV&A) plan and its proper execution are crucially important for the successful accreditation of a modeling and simulation (M&S) application. We provide guidance in developing and executing such a plan throughout the entire M&S application development life cycle. The U.S. Department of Defense (DoD) is the largest sponsor and user of modeling and simulation applications in the world. DoD uses many different types of M&S applications, consisting of a combination of software, hardware, and humanware, under diverse objectives including acquisition, analysis and training.

Computational modeling and wave propagation in media with inelastic deforming microstructure

Abstract: A phenomenological continuum model for computational use has been developed to describe large amplitude transient wave propagation in heterogeneous multi-component materials. A key feature of the model is a physics-based treatment of the continuum response of microstructural components with markedly dissimilar elasticity and strength properties. A fundamental premise of the modeling effort is reliance solely on widely available dynamic material property data including Hugoniot equation-of-state and Hopkinson pressure bar strength data through either direct application or physically plausible theories. Average nonlinear iso-pressure and iso-strain solutions provide bounding responses of the multi-component material. Compressive deformation under pressure and concomitant dissipation is treated through methods of irreversible phase transformation. The model has been incorporated into a multidimensional Eulerian finite-difference shock physics code and used to examine the response of selected materials to dynamic loads.

Turbulent kinetic energy transport in a corner formed by a solid wall and a free surface

Abstract: High-resolution DPIV and LDV measurements were made in a turbulent mixed- boundary corner, i.e. a turbulent boundary layer generated by horizontal flow of water along a vertical wall in the vicinity of a horizontal free surface. This work is an extension of an earlier numerical/experimental study which established the existence of inner and outer secondary flow regions in the corner. The inner secondary motion is characterized by a weak, slowly evolving vortex with negative streamwise vorticity. The outer secondary motion is characterized by an upflow along the wall and outflow away from the wall at the free surface. The objective of the current investigation, then, was to understand the combined effects of a horizontal, shear-free, free surface and a vertical, rigid, no-slip boundary on turbulent kinetic energy transport. The context of this work is providing physical insights and quantitative data for advancing the state of the art in free-surface turbulence modelling. Experiments were conducted in a large free-surface water tunnel at momentum-thickness Reynolds numbers, Reθ, of 670 for the DPIV studies, and 1150 for the LDV measurements. A high-resolution, two-correlation DPIV program was used to generate ensembles of vector fields in planes parallel to the free surface. These data were further processed to obtain profiles of turbulent kinetic energy transport terms, such as production and dissipation. In addition, profiles of streamwise and surface-normal velocity were made (as functions of distance from the wall) using two-component LDV. Key findings of this study include the fact that both turbulent kinetic energy production and dissipation are dramatically reduced close to the free surface. Far from the wall, this results in an increase in surface-parallel uctuations very close to the free surface. The degree of this anisotropy and the spatial scales over which it exists are critical data for improved free-surface turbulence models.

Well-defined intended uses: an explicit requirement for accreditation of modeling and simulation applications

Abstract: A modeling and simulation (M&S) application is built for a specific purpose and its acceptability assessment is carried out with respect to that purpose The accreditation decision for an M&S application is also made with respect to that purpose The purpose is commonly expressed in terms of intended uses The quality of expressing the intended uses significantly affects the quality of the acceptability assessment as well as the quality of making the accreditation decision The purpose of this paper is to provide guidance in proper definition of the intended uses It uses an M&S application for simulating the US National Missile Defense (NMD) system design as an example to illustrate the definition of the intended uses

Origins of total-dose response variability in linear bipolar microcircuits

Abstract: LM111 voltage comparators exhibit a wide range of total-dose-induced degradation. Simulations show this variability may be a natural consequence of the low base doping of the substrate PNP (SPNP) input transistors. Low base doping increases the SPNPs collector to base breakdown voltage, current gain, and sensitivity to small fluctuations in the radiation-induced oxide defect densities. The build-up of oxide trapped charge (N/sub OT/) and interface traps (N/sub IT/) is shown to be a function of pre-irradiation bakes. Experimental data indicate that, despite its structural similarities to the LM111, irradiated input transistors of the LM124 operational amplifier do not exhibit the same sensitivity to variations in pre-irradiation thermal cycles. Further disparities in LM111 and LM124 responses may result from a difference in the oxide defect build-up in the two part types. Variations in processing, packaging, and circuit effects are suggested as potential explanations.

Feature sets for nonstationary signals derived from moments of the singular value decomposition of Cohen-Posch (positive time-frequency) distributions

Abstract: This article presents a new method for determining the principal features of a nonstationary time series process based on the singular value decomposition (SVD) of the Cohen-Posch (1985) positive time-frequency distribution. This new method uses density functions derived from the SVD singular vectors to generate moments that are associated with the principal features of the nonstationary process. Since the SVD singular vectors are orthonormal, the vectors whose elements are composed of the squared elements of the SVD vectors are discrete density functions. Moments generated from these density functions are the principal features of the nonstationary time series process. The main reason for determining features of a time series process is to characterize it by a few simple descriptors.

Transition Onset Prediction for High-Speed Flow

Abstract: An approach that treats nonturbulent e uctuations in a turbulencelike manner and determines onset and extent of transition as part of a e ow calculation isused to study transition athigh Mach numbers. Threesetsof previously obtained experimental data involving straight and e ared cones at zero angle of attack are used to calibrate and validate the model. Two sets, at Mach numbers 3.5 and 6, were carried out in quiet tunnels, and the third set was carried out at a Mach number of 8 in a conventional tunnel. The results suggest that the second mode is not the only mode responsible for transition at high Mach numbers. In general, fair to good agreement with measured recovery factors, adiabatic wall temperatures, and heat-transfer rates is indicated.

Scattering of electromagnetic waves by a perfectly conducting cylinder with a thin lossy magnetic coating

Abstract: We study the scattering interaction of electromagnetic (EM) waves with an infinite cylinder coated with a lossy dielectric material with frequency-dependent material properties. These properties are hypothetical, yet representative of a wide class of available materials. The monostatic and bistatic scattered widths (SW) are evaluated for the TM or TE polarization cases. These calculations require the use of algorithms to evaluate Bessel-Hankel functions of complex arguments. These algorithms are based on a continued fraction approach, which ensures stability of the recursion relations. The bistatic plots of the TM and TE scattering widths for the coated body are displayed in a convenient color-graded scale. The reductions in the scattering widths produced by this type of coating are determined in selected frequency bands and angular sectors, in both polarization cases. It is quantitatively shown how curvature and polarization shift the effectiveness band of the coating. The determined regions in which the SW are minimally affected are the most suitable for target identification purposes.

Acoustic scattering by a three-dimensional elastic object near a rough surface

Abstract: The ensemble-averaged field scattered by a smooth, bounded, elastic object near a penetrable surface with small-scale random roughness is formulated. The formulation consists of combining a perturbative solution for modeling propagation through the rough surface with a transition (T-) matrix solution for scattering by the object near a planar surface. All media bounding the rough surface are assumed to be fluids. By applying the results to a spherical steel shell buried within a rough sediment bottom, it is demonstrated that the ensemble-averaged “incoherent” intensity backscattered by buried objects illuminated with shallow-grazing-angle acoustic sources can be well enhanced at high frequencies over field predictions based on scattering models where all environmental surfaces are planar. However, this intensity must compete with the incoherent intensity scattered back from the interface itself, which can defeat detection attempts. The averaged “coherent” component of the field maintains the strong evanes...

Unsteady analysis of the air wake over the lpd-17

Abstract: An unsteady analysis of the air wake over a Navy vessel, the LPD-17, is performed using FAST3D. FAST3D, developed at the U.S. Naval Research Lab, employs a flux corrected transport algorithm and is capable of solving the unsteady compressible Euler equations on parallel architectures. The code is applied to the air wake of the LPD-17 to quantify the unsteady velocity field over the aft deck of the ship. Two cases are studied: 0 deg and 30 deg wind angles. The computations are compared to experimental data collected in the 8-xlO ft Subsonic Wind Tunnel at the Naval Surface Warfare Center, Carderock Division. Computational and experimental time histories are collected at 500 Hz on a 3-D grid at 279 locations above the aft portion of the deck. The experimental data were collected using hot-film anemometers. The time histories are transformed into the frequency domain to determine the spectral content of the velocity fluctuations. This effort represents a thorough analysis of the unsteady air wake over a detailed geometric model of a typical naval transport vessel and represents a significant contribution to understanding the characteristics of ship air wakes.

Power flow in coupled bending and longitudinal waves in beams

Abstract: In complex structures, curvature and impedance discontinuities (e.g., junctions) couple bending and longitudinal waves. Propagation losses for longitudinal waves are often much less than losses for bending waves, and damping treatments often less effective on longitudinal waves. When the dissipation in longitudinal waves is less than that on bending waves, longitudinal waves can provide an efficient means of power flow between bending waves generated at one location and bending waves that are a source of acoustic radiation at another location. In order to design and locate effective treatments, knowledge of the power flow in longitudinal as well as bending waves is required. The measurement of power in both bending and longitudinal waves when both waves are present is demonstrated. Measurements conducted on a straight beam and a T-beam are compared to predictions obtained using finite element methods. The effect of coupling between waves at the junction in a T-beam is illustrated using results from measurements of power flow.

Direct Method for Optimization of a Centrifugal Compressor Vaneless Diffuser

Abstract: A Direct Method for Optimization (DMO) is developed for investigating pressure rise and energy loss in a vaneless diffuser of a generic compressor used in shipboard air-conditioning systems. The scheme uses Reynolds Averaged Navier-Stokes (RANS) results and evaluates gradients of a predetermined objective function. The current Direct Method for Optimization differs from the popular Inverse Design Method in the process of obtaining final configurations and in the final configurations obtained. The Direct Method for Optimization achieves a final shape from maximizing/minimizing a nonlinear function; i.e., the objective function. Both gradient and non-gradient Direct Methods for Optimization are compared with respect to accuracy and efficiency.The coupled DMO/RANS optimization code is benchmarked using a plane turbulent diffuser also investigated by Zhang et al. using an adjoint method. The benchmark indicates that if a global optimum exists, the result should be independent of the methodologies or design parameters used.The DMO/RANS method is applied to redesign a 3-D centrifugal vaneless diffuser used in a modern generic compressor. The objective function is a composite function of the diffuser’s pressure rise and total energy loss. The new optimum diffuser has a minimum width at a location far beyond the conventional diffuser pinch point. The new diffuser also provides an efficient section for pressure recovery, which takes place after the minimum width location. Test data for the new diffuser validates the current approach at the design condition. Furthermore, improved performance is also recorded experimentally at off-design conditions for the optimized diffuser.Copyright © 2000 by ASME

Acoustic optic hybrid (AOH) sensor

Abstract: The ability of laser vibrometers to receive and process acoustic echoes from the water surface above a submerged target is established and evaluated. Sonar echoes from a submerged target are collected from the water surface by a laser vibrometer. Feasibility of this approach to sensing underwater sound is demonstrated. If the acoustic excitation at an otherwise undisturbed water surface is 195 to 168 dB re: 1 μPa, signal-to-noise ratio (SNR), at the vibrometer output, is shown to range from about 46 to 6 dB. Capillary waves and gravity waves at the water surface are expected and shown to have some destructive effect on the process of echo retrieval. A series of experiments to quantify the surface wave effects is described. The wave experiment results are reported. A successful attempt to acquire echoes from a submerged target over a grid of points for further processing into a three-dimensional image is made and described. The data acquisition and beamforming techniques constitute a three-dimensional, aco...