Showing papers by "Naval Surface Warfare Center published in 2017"
TL;DR: In this paper, the main goal of such a stirring mechanism is to generate an amplitude-varying electromagnetic field that is ideally statistically uniform, which is the goal of the RC.
Abstract: Reverberation chambers (RC), a name inspired in room acoustics, are also known in literature as reverberating, reverb, mode-stirred or mode-tuned chambers. In their basic form, they consist of a shielded metallic enclosure, forming a cavity resonator, together with some mode-stirring mechanism. The main goal of such stirring mechanism is to generate an amplitude-varying electromagnetic field that is ideally statistically uniform.
89 citations
Naval Postgraduate School1, Naval Surface Warfare Center2, University of Colorado Boulder3, Ohio State University4, University of Notre Dame5, United States Army Research Laboratory6, University of California, San Diego7, Office of Naval Research8, United States Naval Research Laboratory9, Johns Hopkins University Applied Physics Laboratory10, University of California, Irvine11, Skidaway Institute of Oceanography12, Oregon State University13, University of Minnesota14
TL;DR: In this article, a CapsuleCASPER objective is to improve the capability to characterize the propagation of radio frequency (RF) signals through the marine atmosphere with coordinated efforts in data collection, data analyses, and modeling of the air-sea interaction processes, refractive environment, and RF propagation.
Abstract: CapsuleCASPER objective is to improve our capability to characterize the propagation of radio frequency (RF) signals through the marine atmosphere with coordinated efforts in data collection, data analyses, and modeling of the air-sea interaction processes, refractive environment, and RF propagation.
88 citations
01 Dec 2017
TL;DR: This paper presents an automatic target recognition (ATR) approach for sonar onboard unmanned underwater vehicles (UUVs) that can be combined with onboard planning and control systems to develop autonomous UUVs able to search for underwater targets without human intervention.
Abstract: This paper presents an automatic target recognition (ATR) approach for sonar onboard unmanned underwater vehicles (UUVs). In this approach, target features are extracted by a convolutional neural network (CNN) operating on sonar images, and then classified by a support vector machine (SMV) that is trained based on manually labeled data. The proposed approach is tested on a set of sonar images obtained by a UUV equipped with side-scan sonar. Automatic target recognition is achieved through the use of matched filters, while target classification is achieved with the trained SVM classifier based on features extracted by the CNN. The results show that deep learning feature extraction provide better performance compared to using other feature extraction techniques such as histogram of oriented gradients (HOG) and local binary pattern (LBP). By processing images autonomously, the proposed approach can be combined with onboard planning and control systems to develop autonomous UUVs able to search for underwater targets without human intervention.
80 citations
TL;DR: In this article, the reaction intermediates formed during CO oxidation on copper-substituted ceria nanoparticles were investigated by means of in situ spectroscopic techniques and an activity descriptor that rationalizes a trend with other metal substitutes (M0.1Ce0.9O2-x, M = Mn, Fe, Co, Ni).
Abstract: Herein we investigate the reaction intermediates formed during CO oxidation on copper-substituted ceria nanoparticles (Cu0.1Ce0.9O2–x) by means of in situ spectroscopic techniques and identify an activity descriptor that rationalizes a trend with other metal substitutes (M0.1Ce0.9O2–x, M = Mn, Fe, Co, Ni). In situ X-ray absorption spectroscopy (XAS) performed under catalytic conditions demonstrates that O2– transfer occurs at dispersed copper centers, which are redox active during catalysis. In situ XAS reveals a dramatic reduction at the copper centers that is fully reversible under catalytic conditions, which rationalizes the high catalytic activity of Cu0.1Ce0.9O2–x. Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) show that CO can be oxidized to CO32– in the absence of O2. We find that CO32– desorbs as CO2 only under oxygen-rich conditions when the oxygen vacancy is filled by the dissociative adsorption of O2. T...
73 citations
TL;DR: In this paper, an effective liquid conductivity approach has been developed to describe the convective transport modes existing within the melt pool in powder bed additive manufacturing processes and a modified Bond number was calculated by comparing surface tension forces with viscous forces within the melting pool region.
Abstract: An effective liquid conductivity approach has been developed to describe the convective transport modes existing within the melt pool in powder bed additive manufacturing processes. A first principles approach is introduced to derive an effective conductive transport mode that encompasses conduction and advection within the melt pool. A modified Bond number was calculated by comparing surface tension forces with viscous forces within the melt pool region. It was determined, due to the small size scale of melt pools in powder bed processes, that the surface tension gradient driven flow, or the Marangoni effect, is the dominant mass transport phenomenon within the melt pool. Validation was conducted by comparing simulation melt pool widths and depths against experimental measurements for Inconel 718 built at beam powers of 150 W, 200 W and 300 W and a scan speed of 200 mm/s. By introducing the effective liquid conductivity, simulated melt pool widths were up to 50% closer to experimental widths and simulated melt pool depths were up to 80% closer to experimental measurements. Analytic temperature profiles and melt pool dimensions are compared between Ti6Al4V, Stainless Steel 316L, Aluminum 7075 and Inconel 718 built with similar process parameters, while including effective liquid conductivity. The reasons for differences in temperature and melt pool geometry are discussed.
66 citations
TL;DR: In this article, a torsion force was added manually at ∼40% maximum compressive loading force during a modified mechanical pinch test to simulate the internal short circuit of large format Li-ion pouch cells induced by mechanical abuse.
62 citations
TL;DR: In this paper, a 1.0 inch (25.4mm) diameter steel ball with steel plate as a rigid support surface was used to study the mechanical responses of Li-ion cells under compressive loading.
57 citations
TL;DR: In this paper, the impact of an increased dislocation density, due to cold rolling, on β phase precipitation as well as the effect of misorientation on growth and kinetics was investigated.
54 citations
27 Apr 2017
TL;DR: Findings from this work can be used to guide the design of security interfaces such that it caters to people with different expertise levels and does not force users to exercise more cognitive processes than required.
Abstract: Purpose
The purpose of this study is to identify factors that determine computer and security expertise in end users. They can be significant determinants of human behaviour and interactions in the security and privacy context. Standardized, externally valid instruments for measuring end-user security expertise are non-existent.
Design/methodology/approach
A questionnaire encompassing skills and knowledge-based questions was developed to identify critical factors that constitute expertise in end users. Exploratory factor analysis was applied on the results from 898 participants from a wide range of populations. Cluster analysis was applied to characterize the relationship between computer and security expertise. Ordered logistic regression models were applied to measure efficacy of the proposed security and computing factors in predicting user comprehension of security concepts: phishing and certificates.
Findings
There are levels to peoples’ computer and security expertise that could be reasonably measured and operationalized. Four factors that constitute computer security-related skills and knowledge are, namely, basic computer skills, advanced computer skills, security knowledge and advanced security skills, and these are identified as determinants of computer expertise.
Practical implications
Findings from this work can be used to guide the design of security interfaces such that it caters to people with different expertise levels and does not force users to exercise more cognitive processes than required.
Originality/value
This work identified four factors that constitute security expertise in end users. Findings from this work were integrated to propose a framework called Security SRK for guiding further research on security expertise. This work posits that security expertise instrument for end user should measure three cognitive dimensions: security skills, rules and knowledge.
38 citations
TL;DR: In this article, the role of Ni-rich regions in enhancing growth kinetics of thermally stable austenite, formed utilizing a multistep intercritical (Quench-Lamellarization-Tempering) heat treatment for a low-carbon 10 wt pct Ni steel was investigated.
Abstract: Austenite reversion and its thermal stability attained during the transformation is key to enhanced toughness and blast resistance in transformation-induced-plasticity martensitic steels. We demonstrate that the thermal stability of Ni-stabilized austenite and kinetics of the transformation can be controlled by forming Ni-rich regions in proximity of pre-existing (retained) austenite. Atom probe tomography (APT) in conjunction with thermodynamic and kinetic modeling elucidates the role of Ni-rich regions in enhancing growth kinetics of thermally stable austenite, formed utilizing a multistep intercritical (Quench-Lamellarization-Tempering (QLT)-type) heat treatment for a low-carbon 10 wt pct Ni steel. Direct evidence of austenite formation is provided by dilatometry, and the volume fraction is quantified by synchrotron X-ray diffraction. The results indicate the growth of nm-thick austenite layers during the second intercritical tempering treatment (T-step) at 863 K (590 °C), with austenite retained from first intercritical treatment (L-step) at 923 K (650 °C) acting as a nucleation template. For the first time, the thermal stability of austenite is quantified with respect to its compositional evolution during the multistep intercritical treatment of these steels. Austenite compositions measured by APT are used in combination with the thermodynamic and kinetic approach formulated by Ghosh and Olson to assess thermal stability and predict the martensite-start temperature. This approach is particularly useful as empirical relations cannot be extrapolated for the highly Ni-enriched austenite investigated in the present study.
33 citations
TL;DR: A recursive algorithm is presented to restore synchronization in voltage and frequency using ADMM, which results in a more robust secondary control even in the presence of noise, and is analytically derived and verified by the simulated microgrid test system.
Abstract: This paper casts the synchronization phenomena in inverter-based ac microgrids as an optimization problem solved using alternating direction method of multipliers (ADMM). Existing cooperative control techniques are based on the standard voting protocols in multiagent systems, and assume ideal communication among inverters. Alternatively, this paper presents a recursive algorithm to restore synchronization in voltage and frequency using ADMM, which results in a more robust secondary control even in the presence of noise. The performance of the control algorithm, for an islanded microgrid test system with additive noise in communication links broadcasting reference signals and communication links connecting neighboring inverters, is evaluated for a modified IEEE 34-bus feeder system. An upper bound for the deviation due to communication noise from the reference set point is analytically derived and verified by the simulated microgrid test system.
TL;DR: In this paper, a design tool for realizing dielectric structures with spatially varying electromagnetic properties via additive manufacturing (AM) is presented, where space-filling curves are utilized to create tool paths ideal for AM processes.
Abstract: In this paper the authors present a novel design tool for realizing dielectric structures with spatially varying electromagnetic properties via additive manufacturing (AM). To create tool paths ideal for AM processes, space-filling curves were utilized. Using fused deposition modeling (FDM), spatially varying structures were printed that produced a spatially varying relative permittivity. A wide range of varying fill fractions were printed and evaluated, demonstrating good agreement between the simulated and measured results. Furthermore, the authors verified that this design tool can be applied to practical structures by designing, printing and testing a gradient index flat lens.
TL;DR: Experimental results on visual and sonar imagery show that PM-LDA can produce both crisp and soft semantic image segmentations; a capability previous topic modeling methods do not have.
Abstract: Topic models [e.g., probabilistic latent semantic analysis, latent Dirichlet allocation (LDA), and supervised LDA] have been widely used for segmenting imagery. However, these models are confined to crisp segmentation, forcing a visual word (i.e., an image patch) to belong to one and only one topic. Yet, there are many images in which some regions cannot be assigned a crisp categorical label (e.g., transition regions between a foggy sky and the ground or between sand and water at a beach). In these cases, a visual word is best represented with partial memberships across multiple topics. To address this, we present a partial membership LDA (PM-LDA) model and an associated parameter estimation algorithm. This model can be useful for imagery, where a visual word may be a mixture of multiple topics. Experimental results on visual and sonar imagery show that PM-LDA can produce both crisp and soft semantic image segmentations; a capability previous topic modeling methods do not have.
TL;DR: In this article, an analytical model was developed to predict the amount of energy absorbed by each mechanism, ballistic limit, duration of the impact event, through-thickness failure distance, and residual velocity.
TL;DR: While emulsion stability decreased with NaCl concentrations, SDS (anionic surfactant) is more likely to form emulsion as salinity increases, requiring more salinity to coalesce SDS emulsions than Triton X-100 (nonionic surfACTant) emulsion.
Abstract: Chemically stabilized emulsions are difficult to break because of micelle stability. Many physical and chemical processes have been used for emulsion breaking/separation; however, most operational parameters are based on empirical data and bulk analysis. A multiscale understanding of emulsions is required before these processes can advance further. This study utilized needle-type microsensors and confocal laser scanning microscopy (CLSM) for characterizing simulated bilge water emulsions with different types of surfactants (Triton X-100 and sodium dodecyl sulfate [SDS]) under various NaCl concentrations at microscale. Using microsensors, a diffusion process was clearly visualized across the oil/water interface which appears to be related to emulsion formation kinetics and mass transfer. While emulsion stability decreased with NaCl concentrations, SDS (anionic surfactant) is more likely to form emulsion as salinity increases, requiring more salinity to coalesce SDS emulsions than Triton X-100 (nonionic sur...
10 Jan 2017
TL;DR: An additive manufacturing method, laser-based layer-by-layer polymer stereolithography is presented, which is shown to have very good fabrication tolerances, which are necessary for making miniature RF components and narrow-band filters.
Abstract: In this paper, a summary of works in creating truly three-dimensional structures for high-frequency applications will be presented using an additive manufacturing method, laser-based layer-by-layer polymer stereolithography. This polymer stereolithography is shown to have very good fabrication tolerances, which are necessary for making miniature RF components and narrow-band filters. The prototype components using this stereolithography include high-Q resonators, low-loss cavity filters and evanescent-mode filters, antennas, and miniature ion traps for mass spectrometry.
TL;DR: In this paper, a Norwegian University of Science and Technology, Corrosion and Surface Protection, Department of Mechanical and Industrial Engineering MTP, Faculty of Engineering Science and technology-IVT, Trondheim N7491, Norway
Abstract: aNorwegian University of Science and Technology, Corrosion and Surface Protection, Department of Mechanical and Industrial Engineering MTP, Faculty of Engineering Science and Technology—IVT, Trondheim N7491, Norway bNaval Surface Warfare Center Carderock Diviision, Code 613, West Bethesda, Maryland 20817-5700, USA cFontana Corrosion Center, Materials Science, and Engineering Department, The Ohio State University, Columbus, Ohio 43210, USA
TL;DR: The Tropical Air-Sea Propagation Study (TAPS) as discussed by the authors gathered coordinated atmospheric and radio frequency (RF) data, offshore of northeastern Australia, in order to address the question of how well radio wave propagation can be predicted in a clear-air, tropical, littoral maritime environment.
Abstract: The purpose of the Tropical Air–Sea Propagation Study (TAPS), which was conducted during November–December 2013, was to gather coordinated atmospheric and radio frequency (RF) data, offshore of northeastern Australia, in order to address the question of how well radio wave propagation can be predicted in a clear-air, tropical, littoral maritime environment. Spatiotemporal variations in vertical gradients of the conserved thermodynamic variables found in surface layers, mixing layers, and entrainment layers have the potential to bend or refract RF energy in directions that can either enhance or limit the intended function of an RF system. TAPS facilitated the collaboration of scientists and technologists from the United Kingdom, the United States, France, New Zealand, and Australia, bringing together expertise in boundary layer meteorology, mesoscale numerical weather prediction (NWP), and RF propagation. The focus of the study was on investigating for the first time in a tropical, littoral environ...
TL;DR: In this article, an analysis of hourly 30-second acoustic samples obtained from a seafloor hydrophone included manual identification of physical, biological, and human-made acoustic sources and measuring received sound pressure levels.
TL;DR: In this paper, the authors describe a probabilistic assessment technique for ship roll behavior in beam sea conditions, following the work of Kimura and its previous application by the author, probability density function (pdf) of roll response is calculated by combining the moment method with equivalent linearization technique.
Abstract: This paper aims to describe a probabilistic assessment technique for ship roll behavior in beam sea conditions. Here, following the work of Kimura and its previous application by the author, probability density function (pdf) of roll response is calculated by combining the moment method with equivalent linearization technique. Results produced using this method are shown to be in good agreement with Monte Carlo simulation results. Moreover, this procedure is extended to the estimation of the capsizing probability. The final results concerning capsizing probability for the linear damping coefficient case are well correlated to the Monte Carlo simulation results. The advantage of this method is that it does not require a significant amount of computation and it enables the direct assessment of capsizing probability for ships with strongly nonlinear restoring terms.
TL;DR: In this paper, a 4P1S cell array using pulsed discharge and electrochemical impedance spectra (EIS) was used to determine a single-point SoH frequency for the array as a whole.
Abstract: State-of-Health (SoH) is a critical parameter for determining the safe operating area of a battery cell and battery packs to avoid abuse and prevent failure and accidents. Experiments were performed at the US Naval Research Laboratory (NRL) on a 4P1S cell array using pulsed discharge and electrochemical impedance spectra (EIS) to determine a single-point SoH frequency for the array as a whole. Individual cell EIS measurements were taken, as well as measurements of the array as a whole. This work will discuss experimental results to date.
TL;DR: In this paper, a test chamber has been constructed with data recordings including chamber pressure and temperature, battery voltage, current, and surface temperature as functions of time throughout the charging and failure processes.
Abstract: Lithium batteries have a tendency to fail violently under adverse conditions leading to the rapid venting of gas. Overcharge, thermal heating, and a combination of the two conditions are applied here to investigate the gas venting process. A test chamber has been constructed with data recordings including chamber pressure and temperature, battery voltage, current, and surface temperature as functions of time throughout the charging and failure processes. High-speed imaging and schlieren flow visualization are used to visualize the gas venting process. A direct comparison between lithium iron phosphate based K2 26650 and lithium nickel manganese cobalt oxide LG 18650 cells is made through a test series of the three failure methods. Failure under thermal, overcharge, and thermal-overcharge conditions are generally similar in terms of the gas venting process, but are observed to have increasingly energetic failures. The thermal-overcharge abuse condition demonstrates an ability to reconnect via internal short circuit even after an initial electrical failure seen as the refusal to accept charge. This reconnection is associated with a secondary, more energetic failure which can produce weak shock pressure waves.
TL;DR: It is suggested that performance systematically degraded with decreasing speech intelligibility, with the largest drop occurring between 80% and 60%.
TL;DR: In this paper, the impact induced slamming loads experienced by ships and offshore structures using advanced fluid structure interaction methods may be a challenging task involving complex and time consuming engineering solutions, which is the reason why the application of well understood and validated quasi-response approaches remains the most rational alternative used by experts for preliminary design assessment.
TL;DR: In this paper, the authors measured near-surface turbulence generated by rainfall in a wind-wave channel filled with synthetic seawater and found that approximately 0.1-0.3% of the kinetic energy flux from the rain is dissipated in the form of turbulence.
Abstract: We present results from experiments designed to measure near-surface turbulence generated by rainfall. Laboratory experiments were performed using artificial rain falling at near-terminal velocity in a wind–wave channel filled with synthetic seawater. In this first series of experiments, no wind was generated and the receiving seawater was initially at rest. Rainfall rates from 40 to were investigated. Subsurface turbulent velocities of the order of are generated near the interface below the depth of the cavities generated by the rain drop impacts. The turbulence appears independent of rainfall rates. At depth larger than the size of the cavities, the turbulent velocity fluctuations decay as . Turbulent length scales also appear to scale with the size of the impact cavities. In these seawater experiments, a freshwater lens is established at the water surface due to the rain. At the highest rain rate studied, the resulting buoyancy flux appears to lead to a shallower subsurface mixed layer and a slight decrease of the turbulent kinetic energy dissipation. Finally, direct measurements and inertial estimates of the turbulent kinetic energy dissipation show that approximately 0.1–0.3 % of the kinetic energy flux from the rain is dissipated in the form of turbulence. This is consistent with existing freshwater measurements and suggests that high levels of dissipation occur at depths and scales smaller than those resolved here and/or that other phenomena dissipate a considerable amount of the total kinetic energy flux provided by rainfall.
TL;DR: This paper will validate a model of a Hybrid Energy Storage Module with fuzzy logic system-level control under the effects of a transient pulsed power load.
Abstract: Hybrid Energy Storage Modules (HESM) have emerged as a possible energy storage device for naval pulsed power applications [1–6]. A HESM combines energy dense and power dense devices to offer a holistic solution for repetitive loads that are highly transient in nature. Actively controlled power electronic converters are used to regulate the power that flows from each energy storage or generation source to a point of common coupling. In these types of naval applications, it is likely that the system will be comprised of components that are available as commercially off the shelf (COTS) components, though some may be custom designed as well. Combining COTS components in a HESM can be challenging because system-level control must be imposed on top of individual device control. Previous work at the University of Texas at Arlington (UTA) has demonstrated a basic model of a HESM and a fuzzy logic systemlevel controller through software simulation. Building on the work by UTA, this paper will validate a model of a Hybrid Energy Storage Module with fuzzy logic system-level control under the effects of a transient pulsed power load.
TL;DR: The Mixed Odor Delivery Device (MODD) as discussed by the authors was designed allowing canines to train on the odor of mixed explosives while keeping the HME components separate and unmixed, thus alleviating the safety requirements for handling, storing and transporting explosives.
TL;DR: In this article, the authors compared hopcalite/LiOH catalysts to platinum (Pt) based catalysts deposited on Al2O3 and CeO2 supports for CO combustion, tolerance to humid environments and combustion of model refrigerant contaminant molecules, freon 134a and methyl chloride.
Abstract: Catalytic air purification systems are required to maintain desirable levels of contaminants in confined space pollution control applications, such as onboard naval submarines. These systems execute oxygen generation, CO2 removal, and burning of contaminants such as carbon monoxide (CO), and hydrocarbons. Crucial characteristics of the catalytic burners on submarines include high activity toward CO combustion, long-term stability in humid environments, and minimal activity towards the decomposition of trace halogenated compounds (often used as refrigerants) that can form toxic acid gas compounds. Here, we compare currently used hopcalite/LiOH catalysts to platinum (Pt) based catalysts deposited on Al2O3 and CeO2 supports for CO combustion, tolerance to humid environments and combustion of model refrigerant contaminant molecules, freon 134a and methyl chloride. The three catalysts exhibit complete combustion of CO in dry air streams by 110 °C, and no catalyst was found to activate freon 134a up to 400 °C. Pt/Al2O3 and Pt/CeO2 catalysts outperformed hopcalite/LiOH by showing enhanced CO oxidation reactivity in the presence of humidity (hopcalite/LiOH is strongly deactivated when H2O is co-fed), and they are minimally active towards methyl chloride oxidation up to 275 °C, whereas hopcalite/LiOH is active below 200 °C. Pt/CeO2 exhibited higher reactivity for CO oxidation and lower activity for methyl chloride oxidation, as compared to Pt/Al2O3. The results strongly suggest that Pt based catalysts, similar to those used in automotive catalysis, may be excellent replacements for currently utilized hopcalite/LiOH catalysts in naval submarine pollution control applications.
28 Sep 2017
TL;DR: In this article, the authors created team structure though task interdependence and observed teamwork outcomes in the form of affect, behavior, and performance outcomes, and found that human partners received higher affect ratings and elicited significantly more communication from the participant than an autonomous partner.
Abstract: Among groups of humans, the team structure has been argued to be the most effective way for people to organize to accomplish work. Research suggests that humans and autonomous agents can be more effective when working together. However, the drive toward capable autonomous teammates has focused on design characteristics while ignoring the importance of social interactions between teammates. In the present study we created team structure though task interdependence and observed teamwork outcomes in the form of affect, behavior, and performance outcomes. A team structure resulted in improved affect and performance outcomes relative to a non-team structure. However, team structure did not elicit significant behavioral differences. Human partners received higher affect ratings and elicited significantly more communication from the participant than an autonomous partner. These findings suggest that social interactions between humans and autonomous teammates should be an important design consideration. While the...
TL;DR: The authors used canonical analysis of principal coordinates to identify surface properties governing attachment across all five biofouling species and suggested that differentiation of the surfaces was influenced to a comparable or greater extent by the dispersive component of surface energy.
Abstract: Multivariate analyses were used to investigate the influence of selected surface properties (Owens–Wendt surface energy and its dispersive and polar components, static water contact angle, conceptual sign of the surface charge, zeta potentials) on the attachment patterns of five biofouling organisms (Amphibalanus amphitrite, Amphibalanus improvisus, Bugula neritina, Ulva linza, and Navicula incerta) to better understand what surface properties drive attachment across multiple fouling organisms. A library of ten xerogel coatings and a glass standard provided a range of values for the selected surface properties to compare to biofouling attachment patterns. Results from the surface characterization and biological assays were analyzed separately and in combination using multivariate statistical methods. Principal coordinate analysis of the surface property characterization and the biological assays resulted in different groupings of the xerogel coatings. In particular, the biofouling organisms were able to d...