9 Matching Results

Search Results

Advanced search parameters have been applied.

Feasibility of using an east coast facility for collaborative research in atmospheric science

Description: This feasibility study examined the effectiveness and potential of a center for collaborative research in atmospheric science and remote sensing. Strongly related to this effort was the development of a telescope facility by Howard University into an atmospheric observatory and remote sensor test-bed. Several remote sensing techniques were evaluated here and the most promising were further developed. Atmospheric assessment concentrated on aerosols, winds, constituent analysis, and the detection of hazardous agents including biologicals. This mission defined the suite of instrumentation. Being a feasibility study, the scope of the project was limited to examining the state of the technology and pushing it when possible. Research performed in applying laser technology lead to the development and subsequent patent application of a new laser heterodyne amplifier, progress toward the development of a laser probe to determine the range resolved size distribution of aerosols, and studies which may lead to the development of a laser induced fluorescence sensing technique for biologicals in the atmosphere. Research in passive atmospheric sensing helped to motivate a field experiment to better understand atmospheric radiance and radiation transport in three-dimensions.
Date: February 9, 1998
Creator: Molitoris, J. D., LLNL
Partner: UNT Libraries Government Documents Department

Modeling Propagation of Shock Waves in Metals

Description: We present modeling results for the propagation of strong shock waves in metals. In particular, we use an arbitrary Lagrange Eulerian (ALE3D) code to model the propagation of strong pressure waves (P {approx} 300 to 400 kbars) generated with high explosives in contact with aluminum cylinders. The aluminum cylinders are assumed to be both flat-topped and have large-amplitude curved surfaces. We use 3D Lagrange mechanics. For the aluminum we use a rate-independent Steinberg-Guinan model, where the yield strength and shear modulus depend on pressure, density and temperature. The calculation of the melt temperature is based on the Lindermann law. At melt the yield strength and shear modulus is set to zero. The pressure is represented as a seven-term polynomial as a function of density. For the HMX-based high explosive, we use a JWL, with a program burn model that give the correct detonation velocity and C-J pressure (P {approx} 390 kbars). For the case of the large-amplitude curved surface, we discuss the evolving shock structure in terms of the early shock propagation experiments by Sakharov.
Date: August 19, 2005
Creator: Howard, W M & Molitoris, J D
Partner: UNT Libraries Government Documents Department

Pre/post-strike atmospheric assessment system (PAAS)

Description: The Pre/Post-Strike Atmospheric Assessment System was proposed to show the importance of local meteorological conditions in the vicinity of a site suspected of storing or producing toxic agents and demonstrate a technology to measure these conditions, specifically wind fields. The ability to predict the collateral effects resulting from an attack on a facility containing hazardous materials is crucial to conducting effective military operations. Our study approach utilized a combination of field measurements with dispersion modeling to better understand which variables in terrain and weather were most important to collateral damage predictions. To develop the PAAS wind-sensing technology, we utilized a combination of emergent and available technology from micro-Doppler and highly coherent laser systems. The method used for wind sensing is to probe the atmosphere with a highly coherent laser beam. As the beam probes, light is back-scattered from particles entrained in the air to the lidar transceiver and detected by the instrument. Any motion of the aerosols with a component along the beam axis leads to a Doppler shift of the received light. Scanning in a conical fashion about the zenith results in a more accurate and two-dimensional measurement of the wind velocity. The major milestones in the benchtop system development were to verify the design by demonstrating the technique in the laboratory, then scale the design down to a size consistent with a demonstrator unit which could be built to take data in the field. The micro-Doppler heterodyne system we developed determines absolute motion by optically mixing a reference beam with the return signal and has shown motion sensitivity to better than 1 cm/s. This report describes the rationale, technical approach and laboratory testing undertaken to demonstrate the feasibility and utility of a system to provide local meteorological data and predict atmospheric particulate motion. The work described herein was ...
Date: February 3, 1997
Creator: Peglow, S. G., LLNL & Molitoris, J. D., LLNL
Partner: UNT Libraries Government Documents Department

An Experimental Investigation of Detonation Corner-Turning Using High Resolution Radiography

Description: We have performed experiments investigating detonation corner turning over a range of high-explosives including LX-17, Composition B, LX-04 and Tritonal. The primary diagnostic utilized here was a new high-resolution x-ray system that was capable of recording a time sequence of the detonation process as it negotiated the corner of interest and propagated. For LX-17 our data detail the formation of a significant dead-zone. Although the detonation eventually turned the corner in LX-17, the dead zone persisted to late times and evidence exists that it never was consumed by either detonation or fast combustion processes. In LX-17 the detonations ability to corner-turn increases as the density is reduced. Furthermore, lowering the density decreases the size of the dead-zone and alters its shape. The other high-explosives investigated were able to turn the corner immediately with no indication of any dead-zone formation.
Date: July 19, 2006
Creator: Molitoris, J D; Andreski, H G; Garza, R G; Batteux, J D & Souers, P C
Partner: UNT Libraries Government Documents Department

Remote sensing of the atmosphere for environmental assessment and national security

Description: The research performed this year marked the beginning of a collaboration between Howard University and LLNL to advance and apply remote sensing technology to a broad range of applications centered on probing the state of the atmosphere. Central to this research was the evolution of a telescope facility at Howard University into an atmospheric observatory and instrument development test-bed. Our work in applying laser technology to remote sensing helped lead to the development and subsequent patent application of a laser heterodyne amplifier and progress toward the development of a multi-wavelength laser probe to determine the range resolved size distribution of particulate matter and aerosols in the atmosphere. Work performed this year also helped us motivate further studies to understand atmospheric radiance and radiation transport in three-dimensions. Our involvement in these programs as supported by the LLNL Research Collaborations Program for Historically Black College s and Universities is reported here.
Date: June 10, 1999
Creator: Arens, J. F.; Davis, E.; Farah, A.; Molitoris, J. D. & Venable, D.
Partner: UNT Libraries Government Documents Department

Detailed Comparison of Blast Effects in Air and Vacuum

Description: Although blast mitigation is most often achieved with solid shielding, ambient gas pressure can also affect the coupling of shock waves to solid targets. In this work the role of air as an energy transfer medium was examined experimentally by subjecting identical large-area rectangular witness plates to short-range blast effects in air and vacuum ({approx}50 mtorr) at 25 C. The expanding reactant front of 3 kg C4 charges was observed by fast camera to be cylindrically symmetric in both air and vacuum. The horizontal component of the reactant cloud velocity (perpendicular to the witness plates) was constant in both cases, with values of 3.0 and 5.9 km/s for air and vacuum, respectively. As a result of the blast, witness plates were plastically deformed into a shallow dish geometry, with local maxima 30 and 20 mm deep for air and vacuum, respectively. The average plate deflection from the air blast was 11 mm, {approx}10% deeper than the average vacuum plate deflection. Shock pressure estimates were made with a simple impedance-matching model, and indicate peak values in the 30-50 MPa range are consistent with the reactant cloud density and velocity. However, more detailed analysis is necessary to definitely establish the mechanisms by which air couples shock energy to the plates.
Date: July 26, 2007
Creator: Tringe, J W; Molitoris, J D; Garza, R G; Andreski, H G; Batteux, J D; Lauderbach, L M et al.
Partner: UNT Libraries Government Documents Department

RESPONSE OF ALUMINUM SPHERES IN SITU TO DETONATION

Description: Time sequence x-ray imaging was utilized to determine the response of aluminum spheres embedded in a detonating high-explosive cylinder. The size of these spheres ranged from 3/8-inch to 1/32-inch in diameter. These experiments directly observed the response of the spheres as a function of time after interaction with the detonation wave. As the spheres are entrained in the post-detonation flow field, they are accelerating and their velocity profile is complicated, but can be determined from the radiography. Using the aluminum spheres as tracers, radial velocities of order 1.6 mm/us and horizontal velocities of order 0.08 mm/us were measured at early times post detonation. In terms of response, these data show that the largest sphere deforms and fractures post detonation. The intermediate size spheres suffer negligible deformation, but appear to ablate post detonation. Post detonation, the smallest spheres either react, mechanically disintegrate, atomize as a liquid or some combination of these.
Date: March 26, 2010
Creator: Molitoris, J D; Garza, R G; Tringe, J W; Batteux, J D; Wong, B M; Villafana, R J et al.
Partner: UNT Libraries Government Documents Department

MIX and Instability Growth from Oblique Shock

Description: We have studied the formation and evolution of shock-induced mix resulting from interface features in a divergent cylindrical geometry. In this research a cylindrical core of high-explosive was detonated to create an oblique shock wave and accelerate the interface. The interfaces studied were between the high-explosive/aluminum, aluminum/plastic, and finally plastic/air. Pre-emplaced surface features added to the aluminum were used to modify this interface. Time sequence radiographic imaging quantified the resulting instability formation from the growth phase to over 60 {micro}s post-detonation. Thus allowing the study of the onset of mix and evolution to turbulence. The plastic used here was porous polyethylene. Radiographic image data are compared with numerical simulations of the experiments.
Date: July 22, 2011
Creator: Molitoris, J D; Batteux, J D; Garza, R G; Tringe, J W; Souers, P C & Forbes, J W
Partner: UNT Libraries Government Documents Department

Propagation of Reactions in Thermally-damaged PBX-9501

Description: A thermally-initiated explosion in PBX-9501 (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) is observed in situ by flash x-ray imaging, and modeled with the LLNL multi-physics arbitrary-Lagrangian-Eulerian code ALE3D. The containment vessel deformation provides a useful estimate of the reaction pressure at the time of the explosion, which we calculate to be in the range 0.8-1.4 GPa. Closely-coupled ALE3D simulations of these experiments, utilizing the multi-phase convective burn model, provide detailed predictions of the reacted mass fraction and deflagration front acceleration. During the preinitiation heating phase of these experiments, the solid HMX portion of the PBX-9501 undergoes a {beta}-phase to {delta}-phase transition which damages the explosive and induces porosity. The multi-phase convective burn model results demonstrate that damaged particle size and pressure are critical for predicting reaction speed and violence. In the model, energetic parameters are taken from LLNL's thermochemical-kinetics code Cheetah and burn rate parameters from Son et al. (2000). Model predictions of an accelerating deflagration front are in qualitative agreement with the experimental images assuming a mode particle diameter in the range 300-400 {micro}m. There is uncertainty in the initial porosity caused by thermal damage of PBX-9501 and, thus, the effective surface area for burning. To better understand these structures, we employ x-ray computed tomography (XRCT) to examine the microstructure of PBX-9501 before and after thermal damage. Although lack of contrast between grains and binder prevents the determination of full grain size distribution in this material, there are many domains visible in thermally damaged PBX-9501 with diameters in the 300-400 {micro}m range.
Date: March 5, 2010
Creator: Tringe, J W; Glascoe, E A; Kercher, J R; Willey, T M; Springer, H K; Greenwood, D W et al.
Partner: UNT Libraries Government Documents Department