Showing papers by "Naval Surface Warfare Center published in 2013"

Thermal Stability of Li2O2 and Li2O for Li-Air Batteries: In Situ XRD and XPS Studies

Abstract: aDepartment of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA bElectrochemical Energy Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA cNaval Surface Warfare Center, Carderock Division, West Bethesda, Maryland 20817-5700, USA dDepartment of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

Structural Changes of Cobalt-Based Perovskites upon Water Oxidation Investigated by EXAFS

Abstract: While many perovskites remain crystalline during the oxygen evolution reaction (OER) in alkaline media, some highly active perovskites become amorphous. We studied the local structure changes of perovskites LaCoO3, Ba0.5Sr0.5Co0.8Fe0.2O3-δ, and SrCo0.8Fe0.2O3-δ before and after OER by X-ray absorption spectroscopy. No change in either local structure or OER activity was observed for LaCoO3, while considerably enhanced OER activities and the conversion of the local structure from corner-sharing octahedra to edge-sharing octahedra were noted for Ba0.5Sr0.5Co0.8Fe0.2O3-δ and SrCo0.8Fe0.2O3-δ as a result of the OER. Possible processes responsible for the structural change and enhanced OER activities are discussed.

Turn and zigzag maneuvers of a surface combatant using a URANS approach with dynamic overset grids

Abstract: Unsteady Reynolds averaged Navier–Stokes (URANS) computations of standard maneuvers are performed for a surface combatant at model and full scale. The computations are performed using CFDShip-Iowa v4, a free surface solver designed for 6DOF motions in free and semi-captive problems. Overset grids and a hierarchy of bodies allow the deflection of the rudders while the ship undergoes 6DOF motions. Two types of maneuvers are simulated: steady turn and zigzag. Simulations of steady turn at 35° rudder deflection and zigzag 20/20 maneuvers for Fr = 0.25 and 0.41 using constant RPM propulsion are benchmarked against experimental time histories of yaw, yaw rate and roll, and trajectories, and also compared against available integral variables. Differences between CFD and experiments are mostly within 10 % for both maneuvers, highly satisfactory given the degree of complexity of these computations. Simulations are performed also with waves, and with propulsion at either constant RPM or torque. 20/20 zigzag maneuvers are simulated at model and full scale for Fr = 0.41. The full scale case produces a thinner boundary layer profile compared to the model scale with different reaction times and handling needed for maneuvering. Results indicate that URANS computations of maneuvers are feasible, though issues regarding adequate modeling of propellers remain to be solved.

Central Pattern Generator Control of a Tensegrity Swimmer

Abstract: Rhythmic motion employed in animal locomotion is ultimately controlled by neuronal circuits known as central pattern generators (CPGs). It appears that these controllers produce efficient, oscillatory command signals by entraining to an efficient or economic gait via sensory feedback. This property is of great interest in the control of autonomous vehicles. The objective of this study is to experimentally validate synthesized CPG control of a tensegrity swimmer. The prestressed cables in a tensegrity structure provide a method of simultaneous actuation and sensing, analogous to the biological motor control mechanism of regulating muscle stiffness through motoneuron activation and sensing the resulting motion by stretch receptors. A three cell, class 2 tensegrity swimmer is designed and built, and open-loop control tests characterize its swimming performance. We then determine gaits for desired entrainment, and use a graphical design method to construct and test the closed-loop system. Lastly, we perform perturbed tests of the swimmer to illustrate the robustness of CPG control.

Fully Distributed Coordination of Multiple DFIGs in a Microgrid for Load Sharing

Abstract: When wind power penetration is high, the available generation may be more than needed, especially for wind-powered microgrids working autonomously. Because the maximum peak power tracking algorithm may result in a supply-demand imbalance, an alternative algorithm is needed for load sharing. In this paper, a fully distributed control scheme is presented to coordinate the operations of multiple doubly-fed induction generators (DFIGs) in a microgrid. According to the proposed control strategy, each bus in a microgrid has an associated bus agent that may have two function modules. The global information discovery module discovers the total available wind generation and total demand. The load sharing control module calculates the generation reference of a DFIG. The consensus-based algorithm can guarantee convergence for microgrids of arbitrary topologies under various operating conditions. By controlling the utilization levels of DFIGs to a common value, the supply-demand balance can be maintained. In addition, the detrimental impact of inaccurate and outdated predictions of maximum wind power can be alleviated. The generated control references are tracked by coordinating converter controls and pitch angle control. Simulation results with a 5-DFIG microgrid demonstrate the effectiveness of the proposed control scheme.

Isosorbide-methacrylate as a bio-based low viscosity resin for high performance thermosetting applications

Abstract: In recent years, the bio-refining industry has developed a number of cyclic molecules with unique attributes derived from renewable carbohydrate feedstocks. Isosorbide is one such compound that has a distinctive fused bicyclic ring system that provides a scaffold for the development of novel bio-based resin systems. We synthesized isosorbide-methacrylate (IM) by the direct esterification of isosorbide using highly reactive species such as methacryloyl chloride or methacrylic anhydride and a base catalyst. IM is a low viscosity (157 cP) cross-linking resin that free radically reacts to form a thermoset polymer with extent of cure at 85%. The resulting polymer has a Tg greater than 240 °C and main degradation temperature of ∼400 °C. Mechanical test results showed that IM had a modulus of ∼4 GPa and strength of 85 MPa. These thermal and mechanical properties show that IM has a significantly higher temperature operating window than any known vinyl ester resin and has similar performance to expensive high temperature epoxy resins. As such, this material has good potential for use in composite applications where a moderate to high temperature free radical cured polymer matrix is needed.

Time-resolved two-dimensional X-ray densitometry of a two-phase flow downstream of a ventilated cavity

Abstract: To measure the void fraction distribution in gas–liquid flows, a two-dimensional X-ray densitometry system was developed. This system is capable of acquiring a two-dimensional projection with a 225 cm2 area of measurement through 21 cm of water. The images can be acquired at rates on the order of 1 kHz. Common sources of error in X-ray imaging, such as X-ray scatter, image distortion, veiling glare, and beam hardening, were considered and mitigated. The measured average void fraction was compared successfully to that of a phantom target and found to be within 1 %. To evaluate the performance of the new system, the flow in and downstream of a ventilated nominally two-dimensional partial cavity was investigated and compared to measurements from dual-tip fiber optical probes and high-speed video. The measurements were found to have satisfactory agreement for void fractions above 5 % of the selected void fraction measurement range.

Factors influencing the ballistic impact resistance of elastomer-coated metal substrates

Abstract: An experimental study was carried out of various factors affecting the ballistic penetration resistance of elastomer/steel bilayers. For blunt penetrators, the contribution of the coating to performance is optimized using the hardest substrates, front surface placement of the elastomer, and (when normalizing by added weight) thin, ca. 2–3 mm, coatings. These results, none of which are predicted by existing models, evince the marked coupling of coating and substrate in the impact response of the bilayer. We also show that nanoparticle fillers have a modest effect on ballistic performance of polyurea coatings, changing the penetration velocity by a few percent or less. This contrasts with the linear dynamic mechanical behavior, which shows much more significant increases in energy absorption due to nano-reinforcement.

On Measuring Shielding Effectiveness of Sparsely Moded Enclosures in a Reverberation Chamber

Abstract: Recently, there has been great interest in evaluating the shielding effectiveness of physically small enclosures (all linear dimensions between 0.1 and 2 m) using a reverberation chamber. In cases where the enclosure is also electrically small (linear dimensions on the order of a free-space wavelength or less), the enclosure supports only discrete resonant modes whose lineshapes have little or no overlap in frequency. This sparsely moded or “undermoded” cavity poses a number of complex challenges to defining and measuring shielding effectiveness. This study contributes to the development of a measurement process for evaluating shielding effectiveness in electrically small enclosures. Specifically, we demonstrate the performance advantages of a traveling-wave antenna (long-wire probe) as a means of fully sampling the field throughout the volume of the enclosure without the need for multiple, wall-mounted probes. Furthermore, the good impedance match of the long-wire antenna permits a large dynamic range in the shielding effectiveness measurements. A simple and fast test method is presented that is accurate and repeatable, and embodies the desired “dovetailing” of shielding effectiveness values obtained as frequency increases and the enclosure transitions from undermoded to overmoded operation. Finally, a rudimentary statistical analysis is provided to assess typical uncertainties inherent in the shielding effectiveness evaluation.

Experimental Validation of Robust Resonance Entrainment for CPG-Controlled Tensegrity Structures

Abstract: Rhythmic motion employed in animal locomotion is ultimately controlled by neuronal circuits known as central pattern generators (CPGs). It appears that these controllers produce efficient oscillatory command signals by entraining to a resonant gait via sensory feedback. This property is of great interest in the control of autonomous vehicles. In this paper, we experimentally validate synthesized CPG control of tensegrity structures. The prestressed cables in a tensegrity structure provide a method of simultaneous actuation and sensing, analogous to the biological motor control mechanism of regulating muscle stiffness through motoneuron activation and sensing the resulting motion by stretch receptors. A three-cell class-two tensegrity structure is designed, built, and modeled to predict the structure's dynamic response. The models are experimentally validated using open-loop control tests. Next, a simple CPG, called a reciprocal inhibition oscillator (RIO), is designed and synthesized in real time. The RIOs outputs are used as actuation commands, while sensory signals from the tensegrity are fed back to the RIO. Multiple controller configurations are tested to validate an RIO design method developed and reported in a complementary study. Finally, the tensegrity dynamics are perturbed by altering the mass of the tensegrity, and the robustness of RIO control is demonstrated through its ability to entrain to the perturbed system.

Active sensing and damage detection using piezoelectric zinc oxide-based nanocomposites.

Abstract: This study investigated the design and performance of piezoelectric nanocomposite-based interdigitated transducers (IDTs) for active sensing and damage detection. First, thin films that are highly piezoelectric and mechanically flexible were designed by embedding zinc oxide (ZnO) nanoparticles in a poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) piezo-polymer matrix. Second, the suspended nanoparticle solutions were then spin coated onto patterned comb electrodes to fabricate the IDTs. The films were then poled to align their electric domains and to increase their permanent piezoelectricity. Upon IDT fabrication, its sensing and actuation of Lamb waves on an aluminum pipe was validated. These results were also compared to data obtained from commercial Macro Fiber Composite IDT transducers. In the last phase of this work, damage detection was demonstrated by mounting these nanocomposite sensors and actuators (using a pitch-catch setup) onto an aluminum pipe and plate. Damage was simulated by tightening a band clamp around the pipe and by drilling holes in the plate. A damage index calculation was used to compare results corresponding to different levels of damage applied to the plate (i.e., different drilled hole depths), and good correlation was observed. Thus, ZnO/PVDF-TrFE transducers were shown to have the potential for use as piezoelectric transducers for structural health monitoring and damage detection.

Nanoscale Analyses of High-Nickel Concentration Martensitic High-Strength Steels

Abstract: Austenite reversion in martensitic steels is known to improve fracture toughness. This research focuses on characterizing mechanical properties and the microstructure of low-carbon, high-nickel steels containing 4.5 and 10 wt pct Ni after a QLT-type austenite reversion heat treatment: first, martensite is formed by quenching (Q) from a temperature in the single-phase austenite field, then austenite is precipitated by annealing in the upper part of the intercritical region in a lamellarization step (L), followed by a tempering (T) step at lower temperatures. For the 10 wt pct Ni steel, the tensile strength after the QLT heat treatment is 910 MPa (132 ksi) at 293 K (20 °C), and the Charpy V-notch impact toughness is 144 J (106 ft-lb) at 188.8 K (−84.4 °C, −120 °F). For the 4.5 wt pct Ni steel, the tensile strength is 731 MPa (106 ksi) at 293 K (20 °C) and the impact toughness is 209 J (154 ft-lb) at 188.8 K (−84.4 °C, −120 °F). Light optical microscopy, scanning electron and transmission electron microscopies, synchrotron X-ray diffraction, and local-electrode atom-probe tomography (APT) are utilized to determine the morphologies, volume fractions, and local chemical compositions of the precipitated phases with sub-nanometer spatial resolution. The austenite lamellae are up to 200 nm in thickness, and up to several micrometers in length. In addition to the expected partitioning of Ni to austenite, APT reveals a substantial segregation of Ni at the austenite/martensite interface with concentration maxima of 10 and 23 wt pct Ni for the austenite lamellae in the 4.5 and 10 wt pct Ni steels, respectively. Copper-rich and M2C-type metal carbide precipitates were detected both at the austenite/martensite interface and within the bulk of the austenite lamellae. Thermodynamic phase stability, equilibrium compositions, and volume fractions are discussed in the context of Thermo-Calc calculations.

Role of sea salt aerosols in the formation of aromatic secondary organic aerosol: yields and hygroscopic properties

Abstract: Environmental context In the coastal and ocean environment, oil spills and ship movement can produce hazardous, organic aerosols. In this study, the role of sea salt in the formation processes of crude-oil-derived organic aerosols derived was explored, and it was found that sea salt can greatly increase the formation and growth of these toxic aerosols. Understanding of this process is crucial for evaluating the effect of oil spills and ship movements on air quality and human health. Abstract Dual, large (52m3), outdoor chambers were used to investigate the effect of aerosol aqueous phase chemistry on the secondary organic aerosol (SOA) yields of the photooxidation products of aromatic hydrocarbons in the coastal environment. Toluene and 1,3,5-trimethylbenzene were photochemically oxidised in the presence and absence of inorganic seeds (sea salt aerosol (SSA) or NaCl) at low NOx conditions. Overall, the presence of SSA, which was shown to contain water even at low relative humidities (RHs), led to higher SOA yields than the presence of NaCl seeds and the seedless condition. The results suggest that SOA yields in the coastal environment will be higher than those produced in terrestrial environment. To study the effect of SOA formation on the chemical composition of SSA, inorganic species were measured using a particle-into-liquid-sampler coupled to an ion chromatograph. The hygroscopic properties of the SSA internally mixed with SOA were analysed using a Fourier-transform infrared spectrometer. The fresh SSA shows a weak phase transition whereas no clear phase transition appeared in the aged SSA. The depletion of Cl– due to the accommodation of nitric acid and carboxylic acids on the surface of SSA coincides with changes in aerosol hygroscopic properties.

An investigation of the strain rate and temperature effects on the plastic flow stress and ductile failure strain of aluminum alloys 5083-H116, 6082-T6 and a 5183 weld metal

Abstract: This article presents a comprehensive experimental and numerical study to investigate the effects of strain rate and temperature on flow stress and ductile failure strain of three aluminum alloys. The test matrix includes smooth and notched round tensile specimens tested at room temperature (24 ℃) and two elevated temperatures (66 ℃ and 149 ℃), and under different strain rates. For 5083-H116, three loading rates are considered at 24 ℃ and it is found that the flow stress and failure strain are lowest at the intermediate strain rate. At high strain rate, the flow stresses of 5083-H116 and 6082-T6 are higher than the quasi-static loading while the flow stress of the 5183 weld metal remains unchanged; the ductility of the 5XXX alloys shows a significant increase compared to the quasi-static loading while the ductility of 6082-T6 does not change much. The study indicates that the Johnson–Cook plasticity and fracture models can be used to describe the temperature dependencies of the flow stress and the failure...

Achieving electrochemical capacitor functionality from nanoscale LiMn2O4 coatings on 3-D carbon nanoarchitectures

Abstract: Conformal nanoscale coatings of Na+-birnessite manganese oxide (MnOx) produced via redox reaction between aqueous permanganate (NaMnO4·H2O) and the carbon surfaces of fiber-paper-supported carbon nanofoams are converted to LiMn2O4 spinel through topotactic exchange of Na+ for Li+ in the as-deposited lamellar birnessite, followed by mild thermal treatments to complete the transformation to LiMn2O4. The evolution of the birnessite-to-spinel conversion is verified with X-ray diffraction, solid-state nuclear magnetic resonance, X-ray absorption spectroscopy, electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The mild conditions used to convert birnessite to spinel ensure that the conformal nanoscale nature of the oxide coating is retained throughout the macroscopically thick (170 μm) carbon nanofoam substrate during the conversion process. The architecture of the LiMn2O4–carbon nanofoam facilitates rapid ion/electron transport, enabling the LiMn2O4 to insert and extract Li+ from aqueous electrolytes at scan rates as high as 25 mV s−1, and with a relaxation time of 37 s as derived from electrochemical impedance. This architectural expression of nanoscale LiMn2O4 delivers full theoretical capacity (148 mA h g−1) at 2 mV s−1.

A comparison of the human lumbar intervertebral disc mechanical response to normal and impact loading conditions.

Abstract: Thirty-four percent of U.S. Navy high speed craft (HSC) personnel suffer from lower back injury and low back pain, compared with 15 to 20% of the general population. Many of these injuries are specifically related to the intervertebral disc, including discogenic pain and accelerated disc degeneration. Numerous studies have characterized the mechanical behavior of the disc under normal physiological loads, while several have also analyzed dynamic loading conditions. However, the effect of impact loads on the lumbar disc—and their contribution to the high incidence of low back pain among HSC personnel—is still not well understood. An ex vivo study on human lumbar anterior column units was performed in order to investigate disc biomechanical response to impact loading conditions. Samples were subjected to a sequence of impact events of varying duration (Δt = 80, 160, 320, 400, 600, 800, and 1000 ms) and the level of displacement (0.2, 0.5, and 0.8 mm), stiffness k, and energy dissipation ΔE were measured. Impacts of Δt = 80 ms saw an 18–21% rise in k and a 3–7% drop in ΔE compared to the 1000 ms baseline, signaling an abrupt change in disc mechanics. The altered disc mechanical response during impact likely causes more load to be transferred directly to the endplates, vertebral bodies, and surrounding soft tissues and can help begin to explain the high incidence of low back pain among HSC operators and other individuals who typically experience similar loading environments. The determination of a “safety range” for impacts could result in a refinement of design criteria for shock mitigating systems on high-speed craft, thus addressing the low back injury problem among HSC personnel.

Mathematical properties of System Readiness Levels

Abstract: Systems engineers need quantifiable metrics for measuring the readiness of a system. The recently developed System Readiness Level (SRL) is such a metric. SRL is a function of Technology Readiness Level (TRL) and Integration Readiness Level (IRL). The mathematical operations used to define this function have some inherent properties. Four desired mathematical properties of SRL models are developed from these inherent properties and other properties suggested from a review of the literature. Matrix algebra and tropical algebra are discussed in the literature as possible mathematical operations. These mathematical operations are reviewed to determine if they meet the desired properties. Tropical Algebra (TA) is found to inherently meet these desired properties. Future research will be conducted to determine if an SRL model using TA is a viable option. ©2012 Wiley Periodicals, Inc. Syst Eng 16:

Wireless Channel Modeling of Multiply Connected Reverberant Spaces: Application to Electromagnetic Compatibility Assessment

Abstract: Radio-frequency wireless communications and sensor networks are currently being deployed in structures that comprise confined, reflective spaces that are electromagnetically coupled. Such structures are commonly found in aviation, shipping, automotive, and warehousing industries. In this paper, a general time-dependent model is presented whose solutions directly provide key properties of the wireless communications channel in multiply connected reverberant spaces. The model equations can be solved numerically for any number of cavities and for any level (weak or strong) of coupling between the cavities. The wireless channel properties investigated in this paper include power delay profile, rms time delay spread, coherence bandwidth, average received channel power, signal-strength fading statistics, and maximum field environment. Measured and modeled channel properties are presented for two and three coupled, highly multipath spaces. These channel model parameters aid in making electromagnetic compatibility assessments of wireless network emissions in these environments.

Effect of surface coatings on aluminum fuel particles toward nanocomposite combustion

Abstract: Flame front velocity (FFV) of three energetic material composites was measured in order to understand the effects of surface functionalization on aluminum reactivity. Composites were prepared using molybdenum trioxide (MoO3) and aluminum (Al) fuel particles with and without surface functionalization. The surface functionalization consisted of a 5-nm-thick layer (35% by weight) of perfluorotetradecanoic acid (PFTD) bonded to the Al2O3 surface of the Al particles. The first composite consisted of Al functionalized with PFTD and MoO3, the second consisted of Al with MoO3 and added PFTD particles to the same weight percentage as in the Al functionalized PFTD, and the third composite consisted of Al with MoO3. The results showed a dramatic increase in FFV from 100 to 500 m/s resulting from the surface functionalization. The results of the experiments show that the surface functionalized Al composite (Al-PFTD/MoO3) has a reaction rate 2 × than that of the simple Al/MoO3 and 3.5 × than that of the Al/MoO3/PFTD composite.

Role of hardware-in-the-loop simulation testing in transitioning new technology to the ship

Abstract: The hardware-in-the-loop (HIL) simulation approach (both controller HIL and power HIL) potentially offers a solution to several of the challenges presented in transitioning new technology to the fleet. However, the capabilities and limitations of the approach must be carefully considered in crafting the role of these tests into an overall testing program. This paper discusses some of these considerations, along with groundwork being conducted to begin to integrate HIL testing into the overall process, discussing the role that this approach may play.

A wavelet filtering scheme for noise and vibration reduction in high-frequency signal injection-based sensorless control of PMSM at low speed

Abstract: Summary form only given. This paper presents a technique for noise and vibration reduction in low-speed sensorless control algorithm of surface mounted permanent magnet synchronous machines (SM-PMSM). The signal processing involved in high-frequency-based sensorless control algorithms has a significant effect on the vibration and noise accompanying such algorithms. Therefore, a wavelet filtering approach is proposed. This wavelet filter is capable of extracting the position information even at low values of injection voltage amplitude where conventional filters fail to extract the information. This leads to a reduction in the machine's noise and vibration. Furthermore, an optimization using hardware-in-the-loop method based on genetic algorithms was implemented in real time to obtain the optimum value of the injected voltages amplitude and frequency causing the least possible vibration with acceptable position estimation accuracy. Consequently, a significant reduction in vibration and noise was achieved. The proposed techniques were implemented on a 2-hp SM-PMSM motor both experimentally and through simulations. Comparisons between numerical and test results confirm the validity of the proposed techniques.

A small unmanned aerial system (UAS) for coastal atmospheric research: preliminary results from New Zealand

Abstract: Experiments conducted in the low-altitude coastal atmosphere in New Zealand have demonstrated the potential of a new unmanned aerial system (UAS) for meteorological research. The Kahu unmanned aerial vehicle flies autonomously using GPS and pre-programmed waypoints, collecting observations of air temperature and relative humidity that are relayed to a ground-station near-instantaneously. Experiments conducted in the Hauraki Gulf, Auckland, show that the Kahu's radio transmission system can successfully transmit data across the ocean surface at distances up to 25 km. Accuracy of the meteorological data collected by the UAS was assessed via a direct comparison with weather station sensors and radiosonde soundings at heights of up to 500 m in the Bay of Plenty. Close agreement between the UAS, radiosonde and weather station data suggests that the Kahu UAS has considerable scope as a new field research tool in New Zealand, capable of providing reliable atmospheric data that can complement and even su...