Publications

Abstract not provided.

The behavior of carbon fiber aircraft composites was studied in adverse thermal environments. The effects of resin composition and fiber orientation were measured in two test configurations: 102 by 127 millimeter (mm) test coupons were irradiated at approximately 22.5 kW/m{sup 2} to measure thermal response, and 102 by 254 mm test coupons were irradiated at approximately 30.7 kW/m{sup 2} to characterize piloted flame spread in the vertically upward direction. Carbon-fiber composite materials with epoxy and bismaleimide resins, and uni-directional and woven fiber orientations, were tested. Bismaleimide samples produced less smoke, and were more resistant to flame spread, as expected for high temperature thermoset resins with characteristically lower heat release rates. All materials lost approximately 20-25% of their mass regardless of resin type, fiber orientation, or test configuration. Woven fiber composites displayed localized smoke jetting whereas uni-directional composites developed cracks parallel to the fibers from which smoke and flames emanated. Swelling and delamination were observed with volumetric expansion on the order of 100% to 200%. The purpose of this work was to provide validation data for SNL's foundational thermal and combustion modeling capabilities.

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Transportation accidents frequently involve liquids dispersing in the atmosphere. An example is that of aircraft impacts, which often result in spreading fuel and a subsequent fire. Predicting the resulting environment is of interest for design, safety, and forensic applications. This environment is challenging for many reasons, one among them being the disparate time and length scales that must be resolved for an accurate physical representation of the problem. A recent computational method appropriate for this class of problems has been developed for modeling the impact and subsequent liquid spread. This involves coupling a structural dynamics code to a turbulent computational fluid mechanics reacting flow code. Because the environment intended to be simulated with this capability is difficult to instrument and costly to test, the existing validation data are of limited scope, relevance, and quality. A rocket sled test is being performed where a scoop moving through a water channel is being used to brake a pusher sled. We plan to instrument this test to provide appropriate scale data for validating the new modeling capability. The intent is to get high fidelity data on the break-up and evaporation of the water that is ejected from the channel as the sled is braking. These two elements are critical to fireball formation for this type of event involving fuel in the place of water. We demonstrate our capability in this paper by describing the pre-test predictions which are used to locate instrumentation for the actual test. We also present a sensitivity analysis to understand the implications of length scale assumptions on the prediction results. Copyright © 2011 by ASME.

Past work has demonstrated the feasibility of pyrolyzing biomass and condensing the resulting vapor to form a low quality combustible liquid. The product, often termed pyrolysis oil, bio-oil, or bio-crude, can be refined to a transportation grade fuel. Because the pyrolysis process is comparatively simple, we speculate that a mobile pyrolysis system might be able to process the biomass at the site of harvest, generating a dense liquid for transportation. This would be expected to result in improved transportation economics compared to transporting the raw biomass fuel. This technology is being considered for northern New Mexico forests that are presently managed by periodic thinning efforts with little utilization of the products. We have designed a bench-scale system and pyrolyzed biomass pellets, which function in these tests as surrogate material for the forest trimmings. The system features controllable furnace temperatures, augur feed, gas recirculation, and multi-stage condensation. We have analyzed gases, chars, and liquids resulting from various operating conditions and report product quantities and qualities through various standard chemical methods. Good liquid mass yields of over 50% of the original material are typically found, with varying product quality and quantity depending on the operating temperature. Our results suggest the current configuration gives better yields and functions more optimally at pyrolysis temperatures around 525°C. For a practical system, combustion of the non-condensable fuel gases may be able to replace the electrically heated furnace used in these tests. Copyright © 2011 by ASME.

Abstract not provided.

Aircraft impacts at flight speeds are relevant environments for aircraft safety studies. This type of environment pertains to normal environments such as wildlife impacts and rough landings, but also the abnormal environment that has more recently been evidenced in cases such as the Pentagon and World Trade Center events of September 11, 2001, and the FBI building impact in Austin. For more severe impacts, the environment is combined because it involves not just the structural mechanics, but also the release of the fuel and the subsequent fire. Impacts normally last on the order of milliseconds to seconds, whereas the fire dynamics may last for minutes to hours, or longer. This presents a serious challenge for physical models that employ discrete time stepping to model the dynamics with accuracy. Another challenge is that the capabilities to model the fire and structural impact are seldom found in a common simulation tool. Sandia National Labs maintains two codes under a common architecture that have been used to model the dynamics of aircraft impact and fire scenarios. Only recently have these codes been coupled directly to provide a fire prediction that is better informed on the basis of a detailed structural calculation. To enable this technology, several facilitating models are necessary, as is a methodology for determining and executing the transfer of information from the structural code to the fire code. A methodology has been developed and implemented. Previous test programs at the Sandia National Labs sled track provide unique data for the dynamic response of an aluminum tank of liquid water impacting a barricade at flight speeds. These data are used to validate the modeling effort, and suggest reasonable accuracy for the dispersion of a non-combustible fluid in an impact environment. The capability is also demonstrated with a notional impact of a fuel-filled container at flight speed. Both of these scenarios are used to evaluate numeric approximations, and help provide an understanding of the quantitative accuracy of the modeling methods.

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We are concerned with transportation accidents and the subsequent fire. Progress is currently being made on a unique capability to model these very challenging events. We have identified Smoothed Particle Hydrodynamics (SPH) as a good method to employ for the impact dynamics of the fluid. SPH is capable of modeling viscous and inertial effects for these impacts for short times. We have also identified our fire code Lagrangian/Eulerian (L/E) particle capability as an excellent method for fuel transport and spray modeling. This fire code can also model the subsequent fire, including details of the heat and mass transfer necessary for thermal environment predictions. These two methods (SPH and L/E) employ disparate but complimentary length and timescales for the calculation, and are suited for coupling given adequate attention to relevant details. Length and timescale interactions are important considerations when joining the two capabilities. Coupling methodologies have been shown to be important to the model accuracy. Focusing on the transfer methods and spatial resolution, a notional impact problem is examined. The outcome helps to quantify the importance of various methods and to better understand the behavior of these modeling methods in a representative environment.

Abstract not provided.

Detailed herein are the results of a validation comparison. The experiment involved a 2 meter diameter liquid pool of Jet-A fuel in a 13 m/s crosswind. The scenario included a large cylindrical blocking object just down-stream of the fire. It also included seven smaller calorimeters and extensive instrumentation. The experiments were simulated with Fuego. The model included several conduction regions to model the response of the calorimeters, the floor, and the large cylindrical blocking object. A blind comparison was used to compare the simulation predictions with the experimental data. The more upstream data compared very well with the simulation predictions. The more downstream data did not compare very well with the simulation predictions. Further investigation suggests that features omitted from the original model contributed to the discrepancies. Observations are made with respect to the scenario that are aimed at helping an analyst approach a comparable problem in a way that may help improve the potential for quantitative accuracy.

Abstract not provided.

The ability of current modeling and simulation tools to accurately predict a building fire of practical size and duration is at issue. Modeling is challenged by computational cost, fidelity of assumed physics, and correct knowledge of initial and boundary conditions. A series of simulations has been conducted to compare with experiments for a fuel fire in a facility. The purpose of the study was to understand the importance of simulation parameters. The test geometry is sufficiently large and the fire of long enough duration to present a challenge to model in detail. Several computational parameters have been varied at magnitudes consistent with the uncertainty in the parameter to determine the parametric sensitivities. The predicted heat flux inside the facility was sensitive to varying degrees to the parameters selected for the study, with those related to the fuel source being the most important physical parameters. Copyright © 2005 by ASME.

A series of experiments has been performed in the Sandia National Laboratories FLAME facility with a 2-meter diameter JP-8 fuel pool fire. Sandia heat flux gages were employed to measure the incident flux at 8 locations outside the flame. Experiments were repeated to generate sufficient data for accurate confidence interval analysis. Additional sources of error are quantified and presented together with the data. The goal of this paper is to present these results in a way that is useful for validation of computer models that are capable of predicting heat flux from large fires. We anticipate using these data for comparison to validate models within the Advanced Simulation and Computing (ASC, formerly ASCI) codes FUEGO and SYRINX that predict fire dynamics and radiative transport through participating media. We present preliminary comparisons between existing models and experimental results.