Showing papers by "Naval Surface Warfare Center published in 2021"

In situ monitoring for fused filament fabrication process: A review

Abstract: Real-time monitoring of the additive manufacturing process offers the promise of guaranteeing product quality and increasing the efficiency of the printing process. This paper summarizes research results for the in situ monitoring of the printing process for the fused filament fabrication process. To have a systematic and comprehensive summary, different methods, devices, and achievements in a range of monitoring systems for 3D printing are described. Sensor types and devices used in the literature for printer health-state monitoring and printing process product quality monitoring are summarized. Discussion of current and future research directions concludes the review.

Instructor strategies to aid implementation of active learning: a systematic literature review

Abstract: Despite the evidence supporting the effectiveness of active learning in undergraduate STEM courses, the adoption of active learning has been slow. One barrier to adoption is instructors’ concerns about students’ affective and behavioral responses to active learning, especially student resistance. Numerous education researchers have documented their use of active learning in STEM classrooms. However, there is no research yet that systematically analyzes these studies for strategies to aid implementation of active learning and address students’ affective and behavioral responses. In this paper, we conduct a systematic literature review and identify 29 journal articles and conference papers that researched active learning, affective and behavioral student responses, and recommended at least one strategy for implementing active learning. In this paper, we ask: (1) What are the characteristics of studies that examine affective and behavioral outcomes of active learning and provide instructor strategies? (2) What instructor strategies to aid implementation of active learning do the authors of these studies provide? In our review, we noted that most active learning activities involved in-class problem solving within a traditional lecture-based course (N = 21). We found mostly positive affective and behavioral outcomes for students’ self-reports of learning, participation in the activities, and course satisfaction (N = 23). From our analysis of the 29 studies, we identified eight strategies to aid implementation of active learning based on three categories. Explanation strategies included providing students with clarifications and reasons for using active learning. Facilitation strategies entailed working with students and ensuring that the activity functions as intended. Planning strategies involved working outside of the class to improve the active learning experience. To increase the adoption of active learning and address students’ responses to active learning, this study provides strategies to support instructors. The eight strategies are listed with evidence from numerous studies within our review on affective and behavioral responses to active learning. Future work should examine instructor strategies and their connection with other affective outcomes, such as identity, interests, and emotions.

Simultaneous Dimensionality and Complexity Model Selection for Spectral Graph Clustering

Abstract: Our problem of interest is to cluster vertices of a graph by identifying underlying community structure. Among various vertex clustering approaches, spectral clustering is one of the most popular m...

Investigation of porosity, texture, and deformation behavior using high energy X-rays during in-situ tensile loading in additively manufactured 316L stainless steel

Abstract: The evolution of damage, texture, and strain in additive manufactured (AM) 316L stainless steel produced via laser powder bed fusion was investigated during in-situ tensile loading using high energy X-rays. Synchrotron X-ray computed tomography (XCT) measurements were performed to determine the initial porosity and monitor the evolution of porosity during tensile loading as well as detect the initiation and growth of voids from pre-existing pore defects in the specimens. The as-built tensile specimens had a cross-sectional area of 1 mm2, which was chosen in order to understand damage behavior in thin-walled structures. Far-field X-ray diffraction measurements were performed to quantify crystallographic texture and the distribution of internal elastic strains during loading. The initial texture from the AM build process had a weak {220} texture aligned parallel to the build direction. As a result of tensile deformation, a strong {111} + {200} double fiber texture develops at high tensile strains and remains until fracture. XCT results confirmed that the inhomogeneous distribution of porosity near the surface played a significant role in damage evolution during tensile loading where voids and cracks initiated at pre-existing pores located within the contour zone. These pores were found to have asymmetric or irregular morphology. At high tensile strains, the massive accumulation of internal damage at these pores eventually connected to the surface reducing the ductility in these thin-walled AM samples and resulting in final failure.

Impact of Interfacial Tension and Critical Micelle Concentration on Bilgewater Oil Separation

Abstract: Oil-in-water emulsions created in shipboard bilgewater can be challenging to treat to hydrocarbon-limiting environmental discharge regulations. While emulsion behavior has been widely studied in other disciplines, research on bilgewater emulsions has been limited due to the variability of bilgewater composition. In this context, surfactant types and concentrations are generally unknown. Therefore, experimental properties of neat surfactants and commercial cleaners were evaluated for predicting bilgewater emulsion stability. Critical micelle concentration (CMC), CMC in the presence of oil (CMCIFT), and equilibrium interfacial tension (IFT) were investigated for emulsion stability using different surfactant types, oil concentrations, and homogenization energies. It was found that CMC was significantly larger in the presence of mineral oil. Γ ∞ values of all three surfactants were similar for the oil-water and air-water cases; however, the κ values were larger for the oil-water interface suggesting that, for a given surfactant, the adsorption of the surfactant molecules to the oil-water interface was more active than to the air-water interface. It was also determined that emulsion stability was most closely related to CMCIFT. Coalescence into a separated oil layer was only observed in emulsion samples with surfactant concentrations below CMCIFT. This relationship was observed for different homogenization intensities and oil concentrations. Experiments also validated the relationship between CMCIFT and oil separation in more complex formulations of commercial cleaners commonly found aboard ships. Four different cleaners with unique compositions all demonstrated separated oil at concentrations below CMCIFT. Overall, CMCIFT represents a practical way to evaluate a cleaner's likelihood of developing stable (> 72 h with no observable oil separation) emulsions in bilgewater.

Hard magnetic properties of FeCoNiAlCuXTiX based high entropy alloys

Abstract: High entropy alloys (HEA) contain multiple principal alloying elements, and possess unique properties due to the high configurational entropy and lattice strain in the system. Ferromagnetic FeCoNi-based HEAs exhibit dramatic changes in crystal structure and the type of magnetism expressed when adding non-magnetic elements such as Al, Cr, Ga, Ti, etc. Interestingly, Alnico permanent magnets also contain multiple principal alloying elements, such as Fe, Co, Ni, and Al, along with other minor additions. This well-studied system is similar in concept to high entropy alloys (HEAs). In this paper, we investigate the hard magnetic properties of FeCoNiAl-based HEAs with additions of Cu/Ti. The addition of Cu/Ti to an equimolar FeCoNiAl alloy is effective at enhancing coercivity, due to spinodal decomposition, but at the expense of saturation magnetization. By varying the ratio of Fe and Co, however, with respect to the other alloying elements, the saturation magnetization is increased, while generally retaining or improving the coercivity. In particular, the Fe2CoNiAlCu0.4Ti0.4 HEA shows promising hard magnetic properties as an isotropic cast magnet, with an HC of 1,078 Oe and (BH)max of 2.06 MGOe, slightly better than the performance of isotropic cast Alnico 2 magnets. The thermal stability is also sufficient for use at elevated temperatures over 200 °C. There was also an interesting increase in high temperature coercivity observed at temperatures from ∼650-800 °C, where these alloys often exhibited higher coercivity than that measured at RT.

3-Phonon Scattering Pathways for Vibrational Energy Transfer in Crystalline RDX.

Abstract: A long-held belief is that shock energy induces initiation of an energetic material through an energy up-pumping mechanism involving phonon scattering through doorway modes. In this paper, a Fermi's golden rule-based 3-phonon theoretical analysis of energy up-pumping in RDX is presented that considers possible doorway pathways through which energy transfer occurs. On average, modes with frequencies up to 102 cm-1 scatter quickly and transfer over 99% of the vibrational energy to other low-frequency modes up to 102 cm-1 within 0.16 ps. These low-frequency modes scatter less than 0.5% of the vibrational energy directly to modes with significant nitrogen-nitrogen (NN) activity. The midfrequency modes from 102 to 1331 cm-1 further up-pump the energy to these modes within 5.6 ps. The highest-frequency modes scatter and redistribute a small fraction of the vibrational energy to all other modes, which last over 2000 ps. The midfrequency modes between 457 and 462 cm-1 and between 831 and 1331 cm-1 are the most critical for vibrational heating of the NN modes and phenomena, leading to initiation in energetics. In contrast, modes stimulated by the shock with frequencies up to 102 cm-1 dominate vibrational cooling of the NN modes.

Ignition and Combustion Characteristics of Al/RDX/NC Nanostructured Microparticles

Abstract: Nanostructured microparticles composed of nanoaluminum, 1,3,5-trinitrohexahydro-s-triazine (RDX), and nitrocellulose (NC) were produced using electrospray assembly and studied in an experimental in...

Effects of Select Metal Oxides on the Onset, Rate and Extent of Low Temperature Ammonium Perchlorate Decomposition

Abstract: Ammonium perchlorate (AP) is the most abundant ingredient in many solid rocket motors and presents a thermal runaway hazard. The addition of metal oxides (MOs) can alter motor performance but may a...

Priority-Based Management of Energy Resources During Power-Constrained Operation of Shipboard Power System

Abstract: It is anticipated that energy storage will play a significant role as increasing numbers of high-power and highly dynamic mission loads are introduced to shipboard systems. The energy magazine (EM) has been proposed as a potential solution for integration of these types of loads, by providing energy storage for buffering dynamics, supplying high power demand over short duration, and providing uninterruptible power system capability. However, the EM also potentially offers the capability to temporarily curtail its power demand, while still serving its loads. In this paper, a rudimentary scheme is described for management of energy resources during periods of power-constrained operation. This approach apportions available power to EMs (or other curtailable loads) based on priority, where the priority of curtailed EMs generally increases over time. Incorporating weights to allow placing higher importance on some EMs and loads, this approach attempts to judiciously allocate scarce power resources, while maintaining service to loads. Simulation results illustrating the approach are also presented.

Effects of support and oxygen vacancies on the energetics of NiO reduction with H2 for the chemical looping combustion (CLC) reaction; a DFT study

Abstract: Chemical looping combustion (CLC) technology is an innovative energy conversion technology that employs oxygen carriers (OC), typically metal oxides, to burn fossil fuels with a minimal carbon footprint. The performance of OCs can be enhanced by the support on which they are deposited through two mechanisms acting at different scales, viz., microstructural and synergetic effects. In this work, the synergetic effect of NiO supported on TiO2 in reaction with hydrogen as a fuel is studied using density functional theory (DFT). Changes in the energetics of the NiO-hydrogen reaction are explained as a consequence of the interaction between the TiO2 support and NiO. The results indicate that the electronic interaction of the TiO2 support with NiO lowers the energy of intermediate states and the energy of the reaction. The effect of TiO2 increases with the creation of more O vacancies as the reaction proceeded. This enhanced reactivity of the NiO-hydrogen reaction is attributed to both an electronic effect of TiO2 and a geometric effect due to O vacancy creation. The synergetic effect of the support on the OC reactions at the atomic level reported here can pave the path to differentiate the electronic and geometric effects and establish the knowledge for the rational design of OC and support systems.

Moving and improving in safety-critical systems: Impacts of head-mounted displays on operator mobility, performance, and situation awareness

Abstract: Mobile displays provide operators in safety-critical systems with real-time information access when tasks require mobility in the working environment. Little empirical work has explored the impact of mobile displays on operator mobility or the impacts of operator mobility on operator performance and situation awareness (SA) in safety-critical settings. This work explores the impacts of head-mounted displays (HMDs) on operators in a real-time physical simulation of maritime navigation. HMD use significantly improved operator performance, SA, and mobility. These results suggest that the contextual information provided to mobile operators by HMDs may reduce information retrieval effort and allow operators to maintain SA without returning to fixed displays. This underscores longstanding training and domain requirements encouraging operator mobility throughout safety-critical systems, indicating a link between increased mobility and improved performance and SA that has not been empirically tested before.

A Thermo-Mechanical Analysis of Laser Hot Wire Additive Manufacturing of NAB

Abstract: There is increased interest in using nickel aluminum bronze (NAB) alloys in large-scale directed energy deposition additive manufacturing (DEDAM) processes for maritime applications, but one challenge lies in the component distortion that results from residual stress generated during fabrication. This paper describes the development and evaluation of thermo-mechanical simulations for laser hot wire (LHW) DEDAM of NAB to predict part distortion. To account for the dearth of temperature-dependent properties for NAB C95800 in open literature and public databases, temperature-dependent material and mechanical properties for NAB C95800 were experimentally measured using test specimens fabricated with a variety of DEDAM processes. Autodesk’s Netfabb Local Simulation software, a commercial finite-element based AM solver, was employed but with its heat source model modified to accommodate LHW DEDAM’s oscillating laser path and additional energy input supplied by the preheated wire feedstock. Thermo-mechanical simulations were conducted using both the acquired temperature-dependent material and mechanical properties and the constant room-temperature properties to assess the impact on simulation accuracy. The usage of constant properties in the thermo-mechanical analysis resulted in significantly different predicted distortion compared to those using the temperature-dependent properties, at times even predicting substrate displacement in an opposite direction.

Examining Port Geometry/Solid Loading for Additively Manufactured Fuels in Hybrid Rockets

Abstract: In this study, the effects of fuel port geometry and fuel additives on the performance characteristics of additively manufactured solid fuels in a hybrid rocket are explored. Static rocket motor fi...

Locally Optimizable Joint Embedding Framework to Design Nitrogen-rich Molecules that are Similar but Improved.

Abstract: Deep learning has shown great potential for generating molecules with desired properties. But the cost and time required to obtain relevant property data have limited study to only a few classes of materials for which extensive data have already been collected. We develop a deep learning method that combines a generative model with a property prediction model to fuse small data of one class of molecules with larger data in another class. Common low-level physicochemical properties are jointly embedded into a latent space that can be used to design molecules in the smaller class. The chemical space around the molecules in the training set is explored through local gradient ascent optimization. Based on nine molecules from the original training set, nine new molecules are found to have improved properties while remaining structurally similar to the training molecules thereby easing requirements for entirely new synthesis routes. Validation is performed using an equilibrium thermochemistry code to verify the molecules and target properties. A specific example targeting the Chapman-Jouguet velocity and small data for nitrogen-rich molecules is shown. Despite the relative lack of nitrogen-rich molecule data, the results demonstrate that fusing and joint embedding with plentiful low nitrogen molecular data can produce higher generative performance than using the scarce data alone.

Cascaded Switching Capacitor based Multi-phase Three-Level Buck Converter for Communication Envelope Tracking

Abstract: The evolution of 4G and 5G communication systems improved not only the data transfer rates but also the losses associated with the radio frequency power amplifier (RFPA) of the transmitter/receiver system. When supplied with a constant DC power source, the RFPA has very poor efficiency. Envelope tracking (ET) is a supply modulation technique where the supply voltage varies dynamically to track the envelope of the input radio frequency (RF) signal. A cascaded switching capacitor-based multi-phase three-level buck converter is proposed in this digest as a drain supply modulator. EPC 8000 family eGaN MOSFETS are used to enable the multi – MHz high switching frequency of operation of the converter. A fourth-order low pass LC-filter is designed to enable the zero-voltage switching and to track the 20 MHz 4G LTE band-limited envelope signal. The proposed converter has a peak efficiency of 97.3 % and over 95 % for most of the output voltage range. Simulation results and preliminary experimental results are provided to validate the proposed concept.