Showing papers by "Naval Surface Warfare Center published in 2010"

Electroless Deposition of Conformal Nanoscale Iron Oxide on Carbon Nanoarchitectures for Electrochemical Charge Storage

Abstract: We describe a simple self-limiting electroless deposition process whereby conformal, nanoscale iron oxide (FeOx) coatings are generated at the interior and exterior surfaces of macroscopically thick (∼90 μm) carbon nanofoam paper substrates via redox reaction with aqueous K2FeO4. The resulting FeOx-carbon nanofoams are characterized as device-ready electrode structures for aqueous electrochemical capacitors and they demonstrate a 3-to-7 fold increase in charge-storage capacity relative to the native carbon nanofoam when cycled in a mild aqueous electrolyte (2.5 M Li2SO4), yielding mass-, volume-, and footprint-normalized capacitances of 84 F g−1, 121 F cm−3, and 0.85 F cm−2, respectively, even at modest FeOx loadings (27 wt %). The additional charge-storage capacity arises from faradaic pseudocapacitance of the FeOx coating, delivering specific capacitance >300 F g−1 normalized to the content of FeOx as FeOOH, as verified by electrochemical measurements and in situ X-ray absorption spectroscopy. The addit...

A Study on the Effect of the Stress State on Ductile Fracture

Abstract: The main purpose of this paper is to demonstrate that besides the stress triaxiality parameter, the Lode angle, which can be related to the third invariant of the deviatoric stress tensor, also has an important effect on ductile fracture. This is achieved by conducting a series of micromechanics analyses of void-containing unit cells and experimental-numerical studies of carefully designed specimens experiencing a wide range of stress states. As a result, a fracture criterion is expressed in terms of the equivalent failure strain as a function of the stress triaxiality and the Lode angle (or the third invariant of the stress deviator) and this function is calibrated for a DH36 steel plate.

Dynamic compression of metallic sandwich structures during planar impulsive loading in water

Abstract: The compressive response of rigidly supported stainless steel sandwich panels subject to a planar impulsive load in water is investigated. Five core topologies that spanned a wide range of crush strengths and strain-dependencies were investigated. They included a (i) square-honeycomb, (ii) triangular honeycomb, (iii) multi-layer pyramidal truss, (iv) triangular corrugation and (v) diamond corrugation, all with a core relative density of approximately 5%. Quasi-statically, the honeycombs had the highest peak strength, but exhibited strong softening beyond the peak strength. The truss and corrugated cores had significantly lower strength, but a post yield plateau that extended to beyond a plastic strain of 60% similar to metal foams. Dynamically, the transmitted pressures scale with the quasi-static strength. The final transmitted momentum increased slowly with core strength (provided the cores were not fully crushed). It is shown that the essential aspects of the dynamic response, such as the transmitted momentum and the degree of core compression, are captured with surprising fidelity by modeling the cores as equivalent metal foams having plateau strengths represented by the quasi-static peak strength. The implication is that, despite considerable differences in core topology and dynamic deformation modes, a simple foam-like model replicates the dynamic response of rigidly supported sandwich panels subject to planar impulsive loads. It remains to ascertain whether such foam-like models capture more nuanced aspects of sandwich panel behavior when locally loaded in edge clamped configurations.

Approximate Analytical Turning Conditions for Underwater Gliders: Implications for Motion Control and Path Planning

Abstract: This paper describes analysis of steady motions for underwater gliders, a type of highly efficient underwater vehicle which uses gravity for propulsion. Underwater gliders are winged underwater vehicles which locomote by modulating their buoyancy and their attitude. Several underwater gliders have been developed and have proven their worth as efficient long-distance, long-duration ocean sampling platforms. Underwater gliders are so efficient because they spend much of their flight time in stable, steady motion. Wings-level gliding flight for underwater gliders has been well studied, but analysis of steady turning flight is more subtle. This paper presents an approximate analytical expression for steady turning motion for a realistic underwater glider model. The problem is formulated in terms of regular perturbation theory, with the vehicle turn rate as the perturbation parameter. The resulting solution exhibits a special structure that suggests an efficient approach to motion control as well as a planning strategy for energy efficient paths.

Synthesis, Processing, and Properties of TaC-TaB2-C Ceramics

Abstract: Multi-phase ceramics in the TaC–TaB 2 –C system were prepared from TaC and B 4 C mixtures by reactive pressureless sintering at 1700–1900 °C. The pressureless densification was promoted by the use of nano-TaC and by the presence of active carbon in the reaction products. The presence of TaB 2 inhibited grain growth of TaC and increased the hardness compared to pure TaC. If a coarse TaC powder was used, the compositions did not densify. In contrast, pure nano-TaC was pressureless sintered at 1800 °C by the addition of 2 wt.% carbon introduced as carbon black or graphite. The introduction of carbon black resulted in fully dense TaC ceramics at temperatures as low as 1500 °C. The grain size of nominally pure TaC ceramics was a strong function of carbon stoichiometry. Enhanced grain size in sub-stoichiometric TaC, compared to stoichiometric TaC, was observed. Additional work is necessary to optimize processing parameters and evaluate the properties of ceramics in the TaC–TaB 2 –C system.

Revision of MIL-HDBK-217, Reliability Prediction of Electronic Equipment

Abstract: This paper will discuss current efforts in the revision of MIL-HDBK-217, Military Handbook, Reliability Prediction of Electronic Equipment. It has been over a decade since this reliability prediction handbook was last updated, yet it remains the most widely used reliability prediction method for electronic equipment. In February 2008, the Defense Standardization Program Office (DSPO) tasked the Crane Division, Naval Surface Warfare Center (NSWC Crane), as the Preparing Activity, to revise MIL-HDBK-217. A plan has been created to refresh the handbook and to look at adding a new approach to better reflect reliability of electronic equipment. A working group of individuals representing Department of Defense (DoD) and industry has been established to conduct this revision. Development and implementation of solutions that reflect industry best practices and DoD needs is critical for success. Results of this task are planned to be new revisions of MIL-HDBK-217. These revisions will provide an updated reliability prediction tool that will assist reliability engineers in performing their work.

Development Process for Custom Three-Dimensional Printing (3DP) Material Systems

Abstract: The development of a new material system for three-dimensional printing (3DP) can be difficult without experience in the field, since the flexibility of the 3DP process implies a large number of material and processing parameters. This paper presents a detailed explanation of the steps involved in developing specific implementations of 3DP, along with tools and insight for each step. This material system development procedure should provide a clear understanding of the 3DP process steps and development decisions to help the user take advantage of the considerable flexibility of 3DP and expedite a new system development. The paper concludes with a demonstration of how the guidance provided is applied in the development of fully dense ceramic dental copings; a research problem uniquely suited to the flexibility of 3DP.

Overview of Self-Magnetically Pinched-Diode Investigations on RITS-6

Abstract: The electron-beam-driven self-magnetically pinched diode is a candidate for future flash X-ray radiographic sources. As presently fielded on Sandia Laboratories' six-cavity Radiographic Integrated Test Stand (RITS-6), the diode is capable of producing sub 3-mm radiation spot sizes and greater than 350 rads of hard X-rays at 1 m. The diode operates between 6 and 7 MV with a slowly decreasing impedance that falls from approximately 65 to 40 Ω during the main pulse. Sensitivity in diode operation is affected by the interaction of evolving plasmas from the cathode and anode, which seem to limit stable diode operation to a narrow parameter regime. To better quantify the diode physics, high-resolution time-resolved diagnostics have been utilized which include plasma spectroscopy, fast-gated imaging, X-ray p-i-n diodes, X-ray spot size, and diode and accelerator current measurements. Data from these diagnostics are also used to benchmark particle-in-cell simulations. An overview of results from experiments and simulations is presented.

Local Damage Detection with the Global Fitting Method Using Operating Deflection Shape Data

Abstract: The present study extends the previous vibration based damage detection method (Yoon et al. in J. Nondestruct. Eval., 2008) by using Operating Deflection Shape (ODS) derived from experimental Frequency Response Function (FRF) data to detect the locations and extent of damage in steel beams, composite beams and plate-like structures. The present method requires to use FRF data obtained only from the damaged structure based on an assumption that the undamaged structure is homogeneous and smooth. The procedure uses the Global Fitting Method (GFM) that fits a smooth and analytic ODS to the measured ODS. Both the analytic and measured ODS are differentiated twice to yield the Curvature Operating Shapes (COS). The Structural Irregularity Index (SII) at each grid point on the structures is the difference between the analytic and measured COS. The procedure is repeated for each frequency in the FRF. Then, SII are averaged over the selected frequencies to obtain the frequency-averaged SII, which are statistically treated to locate damage. The present method is originally developed for one-dimensional (1D) beam models but can be extended further to any two-dimensional (2D) plate-like models by adding the results in the horizontal and/or vertical directions. The present method using experimental FRF successfully identified the locations and extents of the notches in steel beams, delaminations in the composite beams and plates, and dry spots in a composite hull structure. The present method is compared with different damage detection methods and showed improved performance in terms of detecting damage and computation cost. The present method also showed improved performances when ODS rather than mode shapes (MS) data are used.

Effects of automation and task load on task switching during human supervision of multiple semi-autonomous robots in a dynamic environment.

Abstract: The present study assessed the impact of task load and level of automation (LOA) on task switching in participants supervising a team of four or eight semi-autonomous robots in a simulated 'capture the flag' game. Participants were faster to perform the same task than when they chose to switch between different task actions. They also took longer to switch between different tasks when supervising the robots at a high compared to a low LOA. Task load, as manipulated by the number of robots to be supervised, did not influence switch costs. The results suggest that the design of future unmanned vehicle (UV) systems should take into account not simply how many UVs an operator can supervise, but also the impact of LOA and task operations on task switching during supervision of multiple UVs. The findings of this study are relevant for the ergonomics practice of UV systems. This research extends the cognitive theory of task switching to inform the design of UV systems and results show that switching between UVs is an important factor to consider.

Mesoscale Modeling of Boundary Layer Refractivity and Atmospheric Ducting

Abstract: In this study four mesoscale forecasting systems were used to investigate the four-dimensional structure of atmospheric refractivity and ducting layers that occur within evolving synoptic conditions over the eastern seaboard of the United States. The aim of this study was to identify the most important components of forecasting systems that contribute to refractive structures simulated in a littoral environment. Over a 7-day period in April–May of 2000 near Wallops Island, Virginia, meteorological parameters at the ocean surface and within the marine atmospheric boundary layer (MABL) were measured to characterize the spatiotemporal variability contributing to ducting. By using traditional statistical metrics to gauge performance, the models were found to generally overpredict MABL moisture, resulting in fewer and weaker ducts than were diagnosed from vertical profile observations. Mesoscale features in ducting were linked to highly resolved sea surface temperature forcing and associated changes i...

Hybrid wireless hull monitoring system for naval combat vessels

Abstract: There is increasing interest by the naval engineering community in permanent monitoring systems that can monitor the structural behaviour of ships during their operation at sea. This study seeks to reduce the cost and installation complexity of hull monitoring systems by introducing wireless sensors into their architectural designs. Wireless sensor networks also provide other advantages over their cable-based counterparts such as adaptability, redundancy, and weight savings. While wireless sensors can enhance functionality and reduce cost, the compartmentalised layout of most ships requires some wired networking to communicate data globally throughout the ship. In this study, 20 wireless sensing nodes are connected to a ship-wide fibre-optic data network to serve as a hybrid wireless hull monitoring system on a high-speed littoral combat vessel (FSF-1 Sea Fighter). The wireless hull monitoring system is used to collect acceleration and strain data during unattended operation during a one-month period at s...

Motion planning for an autonomous Underwater Vehicle via Sampling Based Model Predictive Control

Abstract: Unmanned Underwater Vehicles (UUVs) can be utilized to perform difficult tasks in cluttered environments such as harbor and port protection. However, since UUVs have nonlinear and highly coupled dynamics, motion planning and control can be difficult when completing complex tasks. Introducing models into the motion planning process can produce paths the vehicle can feasibly traverse. As a result, Sampling-Based Model Predictive Control (SBMPC) is proposed to simultaneously generate control inputs and system trajectories for an autonomous underwater vehicle (AUV). The algorithm combines the benefits of sampling-based motion planning with model predictive control (MPC) while avoiding some of the major pitfalls facing both traditional sampling-based planning algorithms and traditional MPC. The method is based on sampling (i.e., discretizing) the input space at each sample period and implementing a goal-directed optimization (e.g., A★) in place of standard numerical optimization. This formulation of MPC readily applies to nonlinear systems and avoids the local minima which can cause a vehicle to become immobilized behind obstacles. The SBMPC algorithm is applied to an AUV in a cluttered environment and an AUV in a common local minima problem.

A Parametric Model for Characterizing Seabed Textures in Synthetic Aperture Sonar Images

Abstract: High-resolution synthetic aperture sonar (SAS) systems yield finely detailed images of sea bottom environments. SAS image texture models must be capable of representing a wide variety of sea bottom environments including sand ripples, coral or rock formations, and flat hardpack. In this paper, a parameterized model for SAS image textures is derived from the autocorrelation functions (ACFs) of the SAS imaging point spread function (PSF) and the ACF of the seabed texture sonar cross section (SCS). The proposed texture mixture model is analytically tractable and parameterized by component mixing parameters, mixture component correlation lengths, the single-point intensity image statistical shape parameter, and the rotation of the ACF mixture components in the 2-D imaging plane. An iterative parameter estimation algorithm based on the expectation-maximization (EM) algorithm for truncated data is presented and tested against various synthetic and real SAS image textures. The performance of the algorithm is compared and discussed for synthetically generated data across various image sizes and texture characteristics. The model fit is also compared against a small set of real SAS survey images and is shown to accurately fit the imaging PSF and seabed SCS ACF for these textures of interest.

Next-Generation Power and Energy: Maybe Not So Next Generation

Abstract: Through many a technical society paper and/or presentation, such as this, future high-power mission loads such as Electromagnetic Aircraft Launch System, Electromagnetic Rail Gun, and Free Electron Laser that will provide capabilities far greater than can be achieved by existing platforms, have been presented. With these high-power and energy mission loads comes the need for next-generation integrated power systems possessing higher voltage distribution systems (AC or DC), compact/ power-dense conversion modules, high-speed power-dense power generation modules, energy storage modules, and appropriate supervisory and machinery controls to provide and partition the available power and energy to the right load, with the right power and at the right time. This remains the vision for the "Navy after Next" all-electric warship (AEW). However, "Navy Now" and "Next Navy" platforms have challenges and needs that ongoing investments and advanced developments in power and energy technologies can help to meet. Such challenges include reduced dependency on foreign-supplied fossil fuel, increasing demand for installed ship power, controlling ship procurement and life-cycle costs. This paper will present planned and ongoing efforts that can be aligned to meet these nearer term ship challenges, and at the same time, with an eye on the future power and energy requirements when they materialize, be refocused to enable and support the high-power and energy demands of the AEW.

The mean velocity profile of a smooth-flat-plate turbulent boundary layer at high Reynolds number

Abstract: Smooth flat-plate turbulent boundary layers (TBLs) have been studied for nearly a century. However, there is a relative dearth of measurements at Reynolds numbers typical of full-scale marine and aerospace transportation systems (Reθ = Ueθ/ν > 105, where Ue = free-stream speed, θ = TBL momentum thickness and ν = kinematic viscosity). This paper presents new experimental results for the TBL that forms on a smooth flat plate at nominal Reθ values of 0.5 × 105, 1.0 × 105 and 1.5 × 105. Nominal boundary layer thicknesses (δ) were 80–90mm, and Karman numbers (δ+) were 17000, 32000 and 47000, respectively. The experiments were conducted in the William B. Morgan Large Cavitation Channel on a polished (k+ 2δ. To within experimental uncertainty, the measured mean velocity profiles can be fit using traditional zero-pressure-gradient (ZPG) TBL asymptotics with some modifications for the mild favourable pressure gradient. The fitted profile pairs satisfy the von-Karman momentum integral equation to within 1%. However, the profiles reported here show distinct differences from equivalent ZPG profiles. The near-wall indicator function has more prominent extrema, the log-law constants differ slightly, and the profiles' wake component is less pronounced.

Degassing Behavior of Nanostructured Al and Its Composites

Abstract: The synthesis of bulk ultrafine-grained (UFG) and nanostructured Al via cryomilling can frequently require a degassing step prior to consolidation, partly due to the large surface area of the as-milled powders. The objective of this study is to investigate the effects associated with cryomilling with stearic acid additions (as a process-control agent) on the degassing behavior of Al powders. This objective was accomplished by completing select experiments with Al-7.5Mg, Al-6.4 wt pct Al85Ni10La5, and Al-14.3 wt pct B4C. The interaction between Al and stearic acid was determined using thermal analysis combined with Fourier transform infrared spectroscopy (FTIR). The degassing experiments were carried out under high vacuum (10−4 to ~10−6 torr) in a range from room temperature to 400 °C, with the pressure of the released gases monitored using a digital vacuum gage. The results showed that the liberation of chemisorbed water was suppressed in cryomilled Al powders and both the chemisorbed water and stearic acid were primarily released in the form of hydrogen. It was also demonstrated that under certain conditions, a nanostructure (grain size ~100 nm) can be retained following the hot vacuum degassing of cryomilled Al.

Microwave measurements of MgB2: implications for applications and order-parameter symmetry

Abstract: We present measurements of the microwave properties of high-quality thin films of MgB2 deposited by reactive evaporation on both dielectric and metallic substrates. The measurements include those of the surface impedance and the intermodulation distortion (IMD), both as a function of microwave power at temperatures from 1.8 to 35 K. A stripline resonator at 2 GHz is used for the measurements on dielectric substrates and a dielectric resonator at 10.7 GHz is used for the films on metallic substrates. The surface resistance of the MgB2 is lower than that of our sputtered niobium films, and no power dependence was observed up to surface radio-frequency magnetic fields of 400 Oe at 5 K. The temperature dependence of the IMD at low circulating power shows an increase at temperatures T < 10 K that cannot be explained on the basis of s-wave symmetry of the order parameter in both energy gaps. Within the gap-symmetry constraints of the hexagonal crystal symmetry of MgB2, the best fit with our IMD and penetration depth measurements is obtained for the π-gap symmetry given by Δ(, T) = Δ0(T)sin(6), where is the azimuthal angle in the ab plane, and Δ0(T) is a weakly temperature dependent amplitude at low temperatures. This symmetry entails there being six nodal lines.

Acoustic response of unexploded ordnance (UXO) and cylindrical targets

Abstract: A series of monostatic and bistatic acoustic scattering measurements were conducted to investigate discrimination and classification capabilities based on the acoustic response of targets for underwater unexploded ordnance (UXO) applications. The measurements were performed during March 2010 and are referred to as the Pond Experiment 2010 (PondEx10), where the fresh water pond contained a sand sediment. The measurements utilized a rail system with a mobile tower and a stationary sonar tower. Each tower is instrumented with receivers while the sources are located on the mobile tower. For PondEx10, eleven targets were deployed at two distinct ground ranges from the mobile tower system. Acoustic data were initially processed using synthetic aperture sonar (SAS) techniques, and the data were further processed to generate acoustic templates for the target strength as a function of frequency and aspect angle. Preliminary results of the processing of data collected from proud targets are presented. Also presented are the results associated with a processing technique that permits isolation of the response of an individual target, which is in close proximity to other targets.

Impact of Fan Gap Flow on the Centrifugal Impeller Aerodynamics

Abstract: The effect of a gap between an inlet duct and a rotating impeller in a centrifugal fan is often neglected in the impeller design calculations or design-related computational fluid dynamics (CFD) analyses. This leads to an arbitrary determination of the gap size for the final fan configuration. Since the gap guides the volute flow back to the impeller flow field near the shroud high-curvature turning area, the low-momentum jet formed by the gap flow could prevent local flow from separation, reducing the local flow turning losses. However, this jet flow has enlarged flow separation in the blade passage, producing shedding vorticity in the downstream passage-flow. The passage-flow separation and the downstream volute flow, which is also affected by the passage-flow separation, have a higher impact on flow losses than the blade leading edge separation. If the gap size is not selected carefully, the combined effect of the passage-flow separation and downstream volute flow losses reduces the fan’s overall performance between 2% points and 5% points as demonstrated in the current study. In this paper, local impeller velocity distributions obtained from both design-CFD and analysis-CFD calculations are compared along the shroud from the gap to the blade trailing edge. The overall impeller flow fields with and without the gap and volute effects are also compared and discussed based on the CFD solutions. Finally, an example of controlling the gap effect is shown.

Vibrational energy transfer in shocked molecular crystals.

Abstract: We consider the process of establishing thermal equilibrium behind an ideal shock front in molecular crystals and its possible role in initiating chemical reaction at high shock pressures. A new theory of equilibration via multiphonon energy transfer is developed to treat the scattering of shock-induced phonons into internal molecular vibrations. Simple analytic forms are derived for the change in this energy transfer at different Hugoniot end states following shock compression. The total time required for thermal equilibration is found to be an order of magnitude or faster than proposed in previous work; in materials representative of explosive molecular crystals, equilibration is predicted to occur within a few picoseconds following the passage of an ideal shock wave. Recent molecular dynamics calculations are consistent with these time scales. The possibility of defect-induced temperature localization due purely to nonequilibrium phonon processes is studied by means of a simple model of the strain field around an inhomogeneity. The specific case of immobile straight dislocations is studied, and a region of enhanced energy transfer on the order of 5 nm is found. Due to the rapid establishment of thermal equilibrium, these regions are unrelated to the shock sensitivity of a material but may allow temperature localization at high shock pressures. Results also suggest that if any decomposition due to molecular collisions is occurring within the shock front itself, these collisions are not enhanced by any nonequilibrium thermal state.