Showing papers by "Naval Surface Warfare Center published in 2015"

Energetic salts with π-stacking and hydrogen-bonding interactions lead the way to future energetic materials.

Abstract: Among energetic materials, there are two significant challenges facing researchers: 1) to develop ionic CHNO explosives with higher densities than their parent nonionic molecules and (2) to achieve a fine balance between high detonation performance and low sensitivity. We report a surprising energetic salt, hydroxylammonium 3-dinitromethanide-1,2,4-triazolone, that exhibits exceptional properties, viz., higher density, superior detonation performance, and improved thermal, impact, and friction stabilities, then those of its precursor, 3-dinitromethyl-1,2,4-triazolone. The solid-state structure features of the new energetic salt were investigated with X-ray diffraction which showed π-stacking and hydrogen-bonding interactions that contribute to closer packing and higher density. According to the experimental results and theoretical analysis, the newly designed energetic salt also gives rise to a workable compromise in high detonation properties and desirable stabilities. These findings will enhance the future prospects for rational energetic materials design and commence a new chapter in this field.

Online Optimal Generation Control Based on Constrained Distributed Gradient Algorithm

Abstract: In traditional power system, economic dispatch and generation control are separately applied. Online generation adjustment is necessary to regulate generation reference for real-time control to realize economic operation of power systems. Since most economic dispatch solutions are centralized, they are usually expensive to implement, susceptible to single-point-failures, and inflexible. To address the above-mentioned problems, this paper proposed a multi-agent system based distributed control solution that can realize optimal generation control. The solution is designed based upon an improved distributed gradient algorithm, which can address both equality and inequality constraints. To improve the reliability of multi-agent system, the N-1 rule is introduced to design the communication network topology. Compared with centralized solutions, the distributed control solution not only can achieve comparable solutions but also can respond timely when the system experiences change of operating conditions. MAS based real-time simulation results demonstrate the effectiveness of the proposed solution.

Model-Based Systems Engineering

Abstract: Today, we expect our systems to be highly sophisticated, intelligent, intuitive, robust, adaptive, and reliable. As technology, especially computational technology, has increased, so has our ability to imagine and develop even more capable and complex systems. This has progressed to the point where it is rare for an individual to understand all aspects of a system. In fact, it is typical that modern systems are the product of an army of highly trained specialists, each with expertise in traditionally diverse domains. In a modern system, the requirements developer, the mechanical engineer, the programmer, the cost analyst, the manager, and many others must work together to make a system a reality. Modern systems engineering recognizes the necessity of these varied perspectives yet must still achieve efficient and effective systems concepts, designs, implementations, and management. How multiple domains can be organized, managed, and sustained to achieve the development of a useful system is at the heart of systems engineering. In this chapter will discuss how Model-Based Systems Engineering (MBSE) is shifting the emphasis of the system engineering process away from the management of documents to describe a system, to an emphasis on a common, flexible, and persistent model of the system.

History and the Status of Electric Ship Propulsion, Integrated Power Systems, and Future Trends in the U.S. Navy

Abstract: While electric propulsion for warships has existed for nearly a century, it has only been since the end of the Cold War that modern integrated power systems have been developed and implemented on U.S. Navy warships. The principal enablers have been the products of research and development for rotating machines (generators and propulsion motors), power electronics (power conversion and motor drives), energy storage, and controls. The U.S. Navy has implemented this advanced technology incrementally. Notably, DDG 1000 with its integrated propulsion system and CVN 78 with its electromagnetic aircraft launch system will soon join the fleet and mark another important advance to the electric warship. In the future, the integration of electric weapons such as railguns, high power radars, and lasers will result in the final achievement of the electric warship.

Solid-state activation of Li2O2 oxidation kinetics and implications for Li–O2 batteries

Abstract: As one of the most theoretically promising next-generation chemistries, Li–O2 batteries are the subject of intense research to address their stability, cycling, and efficiency issues. The recharge kinetics of Li–O2 are especially sluggish, prompting the use of metal nanoparticles as reaction promoters. In this work, we probe the underlying pathway of kinetics enhancement by transition metal and oxide particles using a combination of electrochemistry, X-ray absorption spectroscopy, and thermochemical analysis in carbon-free and carbon-containing electrodes. We highlight the high activity of the group VI transition metals Mo and Cr, which are comparable to noble metal Ru and coincide with XAS measured changes in surface oxidation state matched to the formation of Li2MoO4 and Li2CrO4. A strong correlation between conversion enthalpies of Li2O2 with the promoter surface (Li2O2 + MaOb ± O2 → LixMyOz) and electrochemical activity is found that unifies the behaviour of solid-state promoters. In the absence of soluble species on charge and the decomposition of Li2O2 proceeding through solid solution, enhancement of Li2O2 oxidation is mediated by chemical conversion of Li2O2 with slow oxidation kinetics to a lithium metal oxide. Our mechanistic findings provide new insights into the selection and/or employment of electrode chemistry in Li–O2 batteries.

Application of Nano-Aluminum/Nitrocellulose Mesoparticles in Composite Solid Rocket Propellants

Abstract: In this work we investigate the potential application of nano-aluminum/nitrocellulose mesoparticles as an ingredient for solid composite rocket propellants. The basic strategy is to incorporate nanoaluminum in the form of a micrometer scale particle containing a gas-generator, to enable easier processing, and potential benefits resulting from reduced sintering prior to combustion. The mesoparticles were made by electrospray and comprised aluminum nanoparticles (50 nm) and nitrocellulose to form micrometer scale particles. In this study, 80 % solids loaded composite propellants (AP/HTPB based) were made with the addition of micrometer sized (2–3 μm) aluminum (10 wt-%), and compared directly to propellants made by directly substituting aluminum mesoparticles for traditional micrometer sized particles. Propellant burning rate was relatively insensitive for mesoparticles containing between 5–15 wt-% nitrocellulose. However, direct comparison between a mesoparticle based propellant, to a propellant containing micrometer scale aluminum particles showed burning rates approximately 35 % higher while having a nearly identical burning rate exponent. High speed imaging indicate that propellants using mesoparticles have less agglomeration of particles on the propellant surface.

Underwater wireless power transfer

Abstract: The feasibility of transferring power over a wide range of distances and orientation offsets has been proven in air for various commercial applications, notably in the electric vehicle industry, by using two loosely-coupled RLC circuits that are tuned to resonate at the same frequency. Key system concepts for resonant wireless power transfer, such as frequency splitting, maximum operating distance, and behavior of the system as it becomes over and under coupled, are well understood theoretically, and demonstrated experimentally. Although prior work on WPT in air is quite extensive and mature, very little research has been conducted on underwater WPT. In particular, no studies have been published describing how basic system concepts vary within a conducting medium such as seawater. In this paper, we report the results of experiments addressing the effects of seawater conductivity on underwater resonant wireless power transfer, compared to the basic system concepts exhibited in air. Results indicate that the losses due to seawater become noticeable for frequencies around 20 kHz, and can be large for frequencies above 50 kHz.

Ignition and Combustion Enhancement of Boron with Polytetrafluoroethylene

Abstract: The ignition and combustion properties of fuel-rich mixtures of boron and polytetrafluorethylene in air and argon were studied as a function of pressure at a heating rate of approximately 1×105 K/s to simulate heating rates that individual ingredients may be subjected to in propellant burning. Mixtures ranging from 20 to 100 wt% boron (balance polytetrafluorethylene) and pressures up to 7 MPa were considered in this study. Ignition of the samples was achieved by joule heating of a platinum filament within a pressure vessel of selected atmospheres. Ignition of the mixture was characterized by monitoring broadband light emission, whereas boron ignition specifically was verified by identification of the BO2 molecule using emission spectroscopy. At atmospheric pressure, none of the mixtures ignited within the duration of the experiment. Mixtures containing more than 80% boron did not consistently ignite under any conditions within the duration of the experiment. It was found that the ignition temperature for...

Repurposing FDA-approved drugs as therapeutics to treat Rift Valley fever virus infection

Abstract: There are currently no FDA-approved therapeutics available to treat Rift Valley fever virus (RVFV) infection. In an effort to repurpose drugs for RVFV treatment, a library of FDA-approved drugs was screened to determine their ability to inhibit RVFV. Several drugs from varying compound classes, including inhibitors of growth factor receptors, microtubule assembly/disassembly, and DNA synthesis, were found to reduce RVFV replication. The hepatocellular and renal cell carcinoma drug, sorafenib, was the most effective inhibitor, being non-toxic and demonstrating inhibition of RVFV in a cell-type and virus strain independent manner. Mechanism of action studies indicated that sorafenib targets at least two stages in the virus infectious cycle, RNA synthesis and viral egress. Computational modeling studies also support this conclusion. siRNA knockdown of Raf proteins indicated that non-classical targets of sorafenib are likely important for the replication of RVFV.

Security Analytics: Essential Data Analytics Knowledge for Cybersecurity Professionals and Students

Abstract: At the 2015 Workshop on Security and Privacy Analytics, there was a well-attended and vigorous debate on educating and training professionals and students in security analytics. This article extends this debate by laying out essential security analytics concepts for professionals and students, sharing educational experiences, and identifying gaps in the field.

Submarine Maneuvers Using Direct Overset Simulation of Appendages and Propeller and Coupled CFD/Potential Flow Propeller Solver

Abstract: This article presents two approaches to simulate maneuvers of a model radio-controlled submarine In the direct simulation approach, rudders, stern planes, and propellers are gridded and treated as moving objects using dynamic overset technology The second approach couples the overset computational fluid dynamics (CFD) solver and a potential flow propeller code, with both codes exchanging velocities at the propeller plane and wake, body forces, and propeller forces and moments, whereas rudders and stern planes are still explicitly resolved It is shown that during the maneuvers, the range of advance coefficients does not deviate much from the design point, making a coupled approach a valid choice for standard maneuvering simulations By allowing time steps about an order of magnitude larger than for the direct simulation approach, the coupled approach can run about five times faster The drawback is a loss of resolution in the wake as the direct propeller simulation can resolve blade vortical structures Open water propeller curves were simulated with both the direct propeller approach and the coupled approach, showing that the coupled approach can match the direct approach performance curves for a wide range of advance coefficients Simulations of a horizontal overshoot maneuver at two approach speeds were performed, as well as vertical overshoot and controlled turn maneuvers at high speed Results show that both CFD approaches can reproduce the experimental results for all parameters, with errors typically within 10%

Synthetic Crystals of Silver with Carbon: 3D Epitaxy of Carbon Nanostructures in the Silver Lattice

Abstract: Noble metals, such as silver, gold, platinum, and palladium, are widely used in many applications due to their high electrical conductivities, high resistance to oxidation and their high malleability. Silver, for example, has the highest ambient electrical (6.3 × 10 7 S m −1 ) and thermal (420 W m −1 K −1 ) conductivities of all metals. Copper is more abundant than noble metals and more economical. It also has high electrical and thermal conductivities. Silver and copper are commonly used in components from consumer electronics to jewelry. However, their practical use and lifetime are limited, or governed by costly maintenance steps, because of their propensity to oxidize or corrode under atmospheric conditions. This is a critical downside in existing applications, as well as a limitation for advanced new applications that require these materials in nanoscale where limited instances of corrosion and/or migration can severely diminish device performance. Cu forms non conducting CuO or Cu 2 O when exposed to the environment. Ag tarnishes by reacting with sulfur [ 1 ] and creating a nonconducting layer of Ag 2 S on the surface of the material, particularly detrimental in nanoscale structures of Ag. [ 2,3 ]

"Insensitive" to touch: fabric-supported lubricant-swollen polymeric films for omniphobic personal protective gear.

Abstract: The use of personal protective gear made from omniphobic materials that easily shed drops of all sizes could provide enhanced protection from direct exposure to most liquid-phase biological and chemical hazards and facilitate the postexposure decontamination of the gear. In recent literature, lubricated nanostructured fabrics are seen as attractive candidates for personal protective gear due to their omniphobic and self-healing characteristics. However, the ability of these lubricated fabrics to shed low surface tension liquids after physical contact with other objects in the surrounding, which is critical in demanding healthcare and military field operations, has not been investigated. In this work, we investigate the depletion of oil from lubricated fabrics in contact with highly absorbing porous media and the resulting changes in the wetting characteristics of the fabrics by representative low and high surface tension liquids. In particular, we quantify the loss of the lubricant and the dynamic contact...

Boron and Polytetrafluoroethylene as a Fuel Composition for Hybrid Rocket Applications

Abstract: A composition consisting of 80% polytetrafluoroethylene and 20% boron (by weight) was considered as a potential high-density solid fuel mixture for mixed hybrid rocket propulsive applications. Constant-pressure strand burner experiments for the given formulation indicated a low-pressure self-deflagration limit of approximately 2.2 MPa (319 psia), and a burning rate correlation rb[cm/s]=0.042(P[MPa])0.531 was determined. Pressurized counterflow burner experiments conducted using pure oxygen revealed formation of surface char, which prevented measurement of solid fuel regression rates below 2 MPa, indicating an additional resistance for heat and mass transfer. Static-fired rocket motor experiments, conducted to determine the pressure and flow dependencies of the system, exhibited characteristic exhaust velocity efficiencies ranging from approximately 86 to 96%. Whereas classical hybrids do not have a strong dependence of fuel regression rate on pressure, a pressure dependence was observed in this system bel...

Capacity Fade of 26650 Lithium-Ion Phosphate Batteries Considered for Use Within a Pulsed-Power System’s Prime Power Supply

Abstract: There is considerable need for a mobile, reliable, efficient, and compact prime power supply for use in a host of directed energy applications. Recent improvements in the energy and power density of electrochemical lithium-ion batteries have made them a very viable option for these types of applications where fast and rep-rate operation is of interest. Despite the proven ability of lithium-ion batteries to source high currents, it is still unclear how they age when they are used to repeatedly source high-rate currents in a pulsed manner, as they must when used in a repetitive rate prime power supply. Similarly, it is unclear how elevated rate recharge affects the life of the battery. Research has been performed at University of Texas at Arlington in which high-power, 2.6 Ah lithium-ion batteries have been repeatedly discharged and recharged at high pulsed rates. This paper will discuss the potential of lithium-ion batteries for use in these applications and will present experimental results performed when two 2.6 Ah cells were both discharged at 28 A (10.8C) and recharged at 9 A (3.5C) to 2.5 and 2.0 V, respectively.

Sonar automatic target recognition for underwater UXO remediation

Abstract: Automatic target recognition (ATR) for unexploded ordnance (UXO) detection and classification using sonar data of opportunity from open oceans survey sites is an open research area. The goal here is to develop ATR spanning real-aperture and synthetic aperture sonar imagery. The classical paradigm of anomaly detection in images breaks down in cluttered and noisy environments. In this work we present an upgraded and ultimately more robust approach to object detection and classification in image sensor data. In this approach, object detection is performed using an in-situ weighted highlight-shadow detector; features are generated on geometric moments in the imaging domain; and finally, classification is performed using an Ada-boosted decision tree classifier. These techniques are demonstrated on simulated real aperture sonar data with varying noise levels.

Design and characterization of an actively controlled hybrid energy storage module for high-rate directed energy applications

Abstract: There is considerable need for a mobile, reliable, efficient, and compact prime power supply for a host of applications, including directed energy and electrical grid backup among others. Electrochemical energy storage devices, which possess either high-power density or high-energy density, have been developed recently and are very applicable for use in these applications. The need for both high energy and high power, however, makes the design and implementation of such a prime power supply a nontrivial task. While lithium-ion batteries (LIBs) are available, which possess both high power and energy density, operation at high power reduces their cycle life, decreasing the reliability and increasing the cost of the system when replacement becomes necessary more frequently. One proposed method involves optimally combining high-energy batteries with high-power electric double layer capacitors (EDLCs) using actively controlled power electronics to regulate the current to and from each respective device. In such a scheme, energy can be slowly sourced to and from the batteries, while the capacitors are used to supply or accept the bulk of the current when the demand is high, especially during fast transients. This type of scheme should not only maximize the batteries' cycle life and ensure that both the energy and power required of the load(s) is always available, but will also increase the instantaneous power capabilities of the system, offering a well-rounded solution to sourcing steady and/or transient loads. When augmenting a fossil fuel generator with a hybrid energy storage module (HESM), the HESM has the ability to act as a high-energy reservoir that can harvest energy from the generator when the loads are in short periods of inactivity. This enables the generator to be continuously base loaded, thereby maintaining a high level of efficiency at all times, while theoretically maintaining the required power quality of the main ac bus. At the University of Texas at Arlington (UTA), an actively controlled, high-rate HESM has been constructed to evaluate its performance under the typical load condition presented by directed energy weapons. It has been assembled using LIBs, EDLCs, and commercial off-the-shelf power electronic converters. A discussion about the future of HESMs, the experimental setup at UTA, and the results obtained thus far will be presented here.

Scattering From Objects at a Water–Sediment Interface: Experiment, High-Speed and High-Fidelity Models, and Physical Insight

Abstract: In March 2010, a series of measurements were conducted to collect synthetic aperture sonar (SAS) data from objects placed on a water–sediment interface. The processed data were compared to two models that included the scattering of an acoustic field from an object on a water–sediment interface. In one model, finite-element (FE) methods were used to predict the scattered pressure near the outer surface of the target, and then this local target response was propagated via a Helmholtz integral to distant observation points. Due to the computational burden of the FE model and Helmholtz integral, a second model utilizing a fast ray model for propagation was developed to track time-of-flight wave packets, which propagate to and subsequently scatter from an object. Rays were associated with image sources and receivers, which account for interactions with the water–sediment interface. Within the ray model, target scattering is reduced to a convolution of a free-field scattering amplitude and an incident acoustic field at the target location. A simulated or measured scattered free-field pressure from a complicated target can be reduced to a (complex) scattering amplitude, and this amplitude then can be used within the ray model via interpolation. The ray model permits the rapid generation of realistic pings suitable for SAS processing and the analysis of acoustic color templates. Results from FE/Helmholtz calculations and FE/ray model calculations are compared to measurements, where the target is a solid aluminum replica of an inert 100-mm unexploded ordnance (UXO).

Underwater Acoustic Navigation Using a Beacon With a Spiral Wave Front

Abstract: In this paper, a method for performing underwater acoustic navigation using a spiral wave-front beacon is examined. A transducer designed to emit a signal whose phase changes by 360 $^{\circ}$ in one revolution can be used in conjunction with a reference signal to determine the aspect of a remote receiver relative to the beacon. Experiments are conducted comparing spiral wave-front beacon navigation to Global Positioning System (GPS) onboard an unmanned surface vehicle. The advantages and disadvantages of several outgoing signals and processing techniques are compared. The most successful technique involves the use of a phased array projector utilizing a broadband signal. Aspect is determined by using a weighted mean over frequencies. Sources of error for each of the techniques are also examined.

Disordered Nanomaterials for Chemielectric Vapor Sensing: A Review

Abstract: Although robust chemical vapor detection by chemielectric point sensors remains as a largely unmet challenge at present, the best performance to date and the most likely avenue for future progress is with sensor designs in which the transductive element is a disordered nanostructured material. We here review the evidence for this claim, with illustrations drawn from recent work on sensors made from gold nanoparticles, carbon nanotubes, and reduced graphene oxide nanoplatelets. These examples can be regarded as being prototypical of disordered nanostructured films formed of primitive objects that are nanoscopic in 3-D, 2-D, and 1-D, respectively.

Semiparametric Statistical Stripmap Synthetic Aperture Autofocusing

Abstract: Autofocusing synthetic aperture imagery by maximizing a statistical quality metric such as contrast or sharpness is a well-documented approach in both synthetic aperture radar (SAR) literature and synthetic aperture sonar literature It is most successfully applied in spotlight-mode SAR applications, where the assumption of spatial invariance of the corrupting phase function is strong and expressions for the gradients of various quality metrics with respect to standard error models have been calculated Examples of application to stripmap imagery often involve sectioning images into small blocks, allowing spotlight algorithms to be patchwise applied This paper formulates the gradient of the cost function in a manner that is consistent with the stripmap error model, inherently providing solutions that compensate for the spatial variance while simultaneously bypassing the need for subdividing an image or aperture This paper formulates the stripmap gradient expression in conjunction with a computationally efficient imaging approach to rapidly achieve metric-maximizing solutions Demonstrations are shown on a widebeam wideband rail-based system experiencing random jitter and on an unmanned-underwater-vehicle-mounted sonar system exhibiting artificially injected crabbing and sway errors Results indicate that the algorithm is particularly effective at compensating for random and rapidly oscillating navigation and jitter errors, as well as sidelobes introduced by crabbing in arrayed systems

Investigation of Ship Topside Modeling Practices for Wind Tunnel Experiments

Abstract: The aerodynamic flow field around a ship’s topside is important to assess ship performance and survivability, evaluate the ship operating envelope, and for launch and recovery of manned and unmanned vehicles. Scaled aerodynamic models of ships are often tested in wind tunnels to measure the topside flow field characteristics. In this study experiments are performed to investigate wind tunnel test practices for modeling ship topside aerodynamics in a general-purpose wind tunnel. Three models of the generic Simple Frigate Shape 2 topside geometry, 4.6, 6.7, and 9.1 feet in length, are used to investigate impacts of Reynolds number, blockage, and wall effects on wind loads and air wake in an 8-by-10-foot wind tunnel. Data collected indicate that blockage effects for the largest model may increase apparent wind loads as much as 20% or more. However, analysis shows that blockage effects can be accounted for using Maskell’s correction for a non-lifting plate. Wall effects also are found to impact wind load and air wake data for large models, specifically models spanning more than two-thirds of the tunnel width in beam-wind conditions. An Atmospheric Boundary Layer (ABL) is simulated by use of an inlet grid system. Wind loads coefficients collected at non-headwind conditions are found to be sensitive to ABL profile, suggesting that physical simulation of ABL is necessary for accurate load measurements.

High Pressure Ignition and Combustion of Aluminum Hydride

Abstract: An experimental study was conducted to determine the high pressure ignition characteristics of α-aluminum hydride. Aluminum hydride particles were heated on a platinum filament at heating rates of approximately 1 × 105 K/s in a pressure vessel for pressures ranging up to about 7 MPa, in order to quantify the ignition temperature and to observe the ignition process. Experiments were conducted in air, argon, and nitrogen as the pressurizing environment. This study revealed that the dehydrogenation of aluminum hydride is not a function of pressure under the conditions tested. In addition, ignition temperatures were found to be approximately linearly related to pressure until pressures exceeded about 0.4 MPa, at which point they remained constant through the highest pressures tested. High speed imaging of the ignition process showed a dramatic change in the ignition behavior for pressures above 0.4 MPa, corresponding to what we believe is a threshold for H2/air autoginition or perhaps even an explosion limit....

Large-eddy simulations of plasma-based asymmetric control of supersonic round jets

Abstract: Localised arc filament plasma actuators are modelled with a validated technique to examine asymmetric control of a perfectly expanded round free jet to deflect its downstream trajectory. The nominal Mach and Reynolds numbers are 1.3 and 1 million, respectively. No-control, symmetrically controlled, and under-expanded jets are also simulated for comparison purposes. Parametric variation of actuation frequency and duty cycle indicate that asymmetric control can alter the trajectory, and, within the confines of the parameters investigated, the optimal forcing scheme was found to correspond to the jet's column-mode frequency and a duty cycle of approximately 60%. Increasing frequency and duty cycle beyond these values have a detrimental effect on control, which is consistent with experimental findings. Asymmetric actuation resulted in significant mixing enhancement on the actuated side, as evidenced by the increased growth rate of the non-dimensional momentum thickness. The effectiveness of control is reduced for under-expanded jet conditions.

Nanocarbon-copper thin film as transparent electrode

Abstract: Researchers seeking to enhance the properties of metals have long pursued incorporating carbon in the metallic host lattice in order to combine the strongly bonded electrons in the metal lattice that yield high ampacity and the free electrons available in carbon nanostructures that give rise to high conductivity. The incorporation of carbon nanostructures into the copper lattice has the potential to improve the current density of copper to meet the ever-increasing demands of nanoelectronic devices. We report on the structure and properties of carbon incorporated in concentrations up to 5 wt. % (∼22 at. %) into the crystal structure of copper. Carbon nanoparticles of 5 nm–200 nm in diameter in an interconnecting carbon matrix are formed within the bulk Cu samples. The carbon does not phase separate after subsequent melting and re-solidification despite the absence of a predicted solid solution at such concentrations in the C-Cu binary phase diagram. This material, so-called, Cu covetic, makes deposition of Cu films containing carbon with similar microstructure to the metal possible. Copper covetic films exhibit greater transparency, higher conductivity, and resistance to oxidation than pure copper films of the same thickness, making them a suitable choice for transparent conductors.

Test methods and response surface models for hot, humid air decontamination of materials contaminated with dirty spores of Bacillus anthracis ∆Sterne and Bacillus thuringiensis Al Hakam.

Abstract: Aims To develop test methods and evaluate survival of Bacillus anthracis ∆Sterne or Bacillus thuringiensis Al Hakam on materials contaminated with dirty spore preparations after exposure to hot, humid air using response surface modelling. Methods and results Spores (>7 log10 ) were mixed with humic acid + spent sporulation medium (organic debris) or kaolin (dirt debris). Spore samples were then dried on five different test materials (wiring insulation, aircraft performance coating, anti-skid, polypropylene, and nylon). Inoculated materials were tested with 19 test combinations of temperature (55, 65, 75°C), relative humidity (70, 80, 90%) and time (1, 2, 3 days). The slowest spore inactivation kinetics was on nylon webbing and/or after addition of organic debris. Conclusions Hot, humid air effectively decontaminates materials contaminated with dirty Bacillus spore preparations; debris and material interactions create complex decontamination kinetic patterns; and B. thuringiensis Al Hakam is a realistic surrogate for B. anthracis. Significance and impact of the study Response surface models of hot, humid air decontamination were developed which may be used to select decontamination parameters for contamination scenarios including aircraft.

Modeling Rotor Unsteady Forces and Sound Due to Homogeneous Turbulence Ingestion

Abstract: An analytical approach is presented to model the broadband unsteady force cross-correlations exerted on a rotor due to a spatially homogeneous turbulent inflow. In addition, the rotor unsteady force cross-correlation matrix is treated as a set of correlated, compact dipole acoustic sources to predict the low-frequency radiated sound field of a subsonic rotor ingesting a turbulent flow. It is shown that turbulence-induced rotor forces in the radial and axial directions are uncorrelated for the special condition when spatially homogeneous turbulence is ingested, and further it is shown that radial-to-axial force correlation can exist when the turbulent inflow velocity field contains a coherent once-per-revolution variation. Equations to estimate rotor turbulence ingestion sound from noncompact dipole sources are also developed for situations when the compact acoustic assumption is invalid. A numerical simulation of the turbulence force and acoustic response for a 10-bladed rotor ingesting a spatially homoge...