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  • 1
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    New Species of Fire Discovered: Fingering Flamelets Form a Dynamic Population (2005)
    In:  CASI
    Details
    Publication Date: 2018-06-02
    Description: Poets and artists have long used fire as a metaphor for life. At the NASA Glenn Research Center, recent experiments in a subcritical Rayleigh number flow channel demonstrated that this analogy holds up surprisingly well when tools developed to characterize a biological population are applied to a class of fire that occurs in near-extinction, weakly convective environments (such as microgravity) or in vertically confined spaces (such as our apparatus). Under these conditions, the flame breaks into numerous 'flamelets" that form a Turing-type reaction-diffusion fingering pattern as they spread across the fuel. It is standard practice on U.S. spacecraft for the astronaut crew to turn off the ventilation to help extinguish a fire, both to eliminate the fresh oxygen supply and to reduce the distribution of the smoke. When crew members think that the fire is fully extinguished, they reactivate the ventilation system to clear the smoke. However, some flamelets can survive, and our experiments have demonstrated that flamelets quickly grow into a large fire when ventilation increases.
    Keywords: Propellants and Fuels
    Type: Research and Technology 2004; NASA/TM-2005-213419
    Format: application/pdf
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  • 2
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    Testing Strategies for Model-Based Development (2006)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This report presents an approach for testing artifacts generated in a model-based development process. This approach divides the traditional testing process into two parts: requirements-based testing (validation testing) which determines whether the model implements the high-level requirements and model-based testing (conformance testing) which determines whether the code generated from a model is behaviorally equivalent to the model. The goals of the two processes differ significantly and this report explores suitable testing metrics and automation strategies for each. To support requirements-based testing, we define novel objective requirements coverage metrics similar to existing specification and code coverage metrics. For model-based testing, we briefly describe automation strategies and examine the fault-finding capability of different structural coverage metrics using tests automatically generated from the model.
    Keywords: Computer Programming and Software
    Type: NASA/CR-2006-214307
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Energy Storage: Batteries and Fuel Cells for Exploration (2007)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: NASA's Vision for Exploration requires safe, human-rated, energy storage technologies with high energy density, high specific energy and the ability to perform in a variety of unique environments. The Exploration Technology Development Program is currently supporting the development of battery and fuel cell systems that address these critical technology areas. Specific technology efforts that advance these systems and optimize their operation in various space environments are addressed in this overview of the Energy Storage Technology Development Project. These technologies will support a new generation of more affordable, more reliable, and more effective space systems.
    Keywords: Propellants and Fuels
    Type: NASA/TM-2007-214837 , AIAA Paper-2007-0541 , E-16051 , 45th Aerospace Sciences Meeting and Exhibit; Jan 08, 2007 - Jan 11, 2007; Reno, NV; United States
    Format: application/pdf
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  • 4
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    Preliminary Appraisal of Ferrocene as an Igniting Agent for JP-4 Fuel and Fuming Nitric Acid (1953)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: A preliminary experimental study was made of the properties of ferrocene as a solute and as a suspension in JP-4 fuel, and of the ignition delays of ferrocene - JP-4 mixture with A.F. specification 14104 white fuming nitric acid (WFNA). The investigation covered concentrations of 4 to 10 percent by weight ferrocene, and a temperature range of -40 to 80 F. The solubility of ferrocene in JP-4 is about 5 percent at room temperature and about 1 percent (extrapolated) at -80 F. The solubility is increased somewhat by increased aromatics content. Undissolved ferrocene particles of 100 mesh and smaller settle rapidly in JP-4. Clear solutions of 4 and 5 percent ferrocene in JP-4 fuels containing 10 and 25 percent by volume aromatics, respectively, do not ignite with WFNA at room temperature. Mixtures containing 10 percent ferrocene (100- mesh and smaller undissolved particles in suspension) ignited with vigorous persistent flames at room temperature, but did not ignite at -38 F. The ignition delays at room temperature, however, were widely varied; the range from 85 milliseconds to over 1 second perhaps reflected differences in degree of sedimentation.
    Keywords: Propellants and Fuels
    Type: NACA-RM-E53H21
    Format: application/pdf
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  • 5
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    Model-Based Safety Analysis (2006)
    In:  CASI
    Details
    Publication Date: 2019-07-11
    Description: System safety analysis techniques are well established and are used extensively during the design of safety-critical systems. Despite this, most of the techniques are highly subjective and dependent on the skill of the practitioner. Since these analyses are usually based on an informal system model, it is unlikely that they will be complete, consistent, and error free. In fact, the lack of precise models of the system architecture and its failure modes often forces the safety analysts to devote much of their effort to gathering architectural details about the system behavior from several sources and embedding this information in the safety artifacts such as the fault trees. This report describes Model-Based Safety Analysis, an approach in which the system and safety engineers share a common system model created using a model-based development process. By extending the system model with a fault model as well as relevant portions of the physical system to be controlled, automated support can be provided for much of the safety analysis. We believe that by using a common model for both system and safety engineering and automating parts of the safety analysis, we can both reduce the cost and improve the quality of the safety analysis. Here we present our vision of model-based safety analysis and discuss the advantages and challenges in making this approach practical.
    Keywords: Computer Programming and Software
    Type: NASA/CR-2006-213953
    Format: application/pdf
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  • 6
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    ADGS-2100 Adaptive Display and Guidance System Window Manager Analysis (2006)
    In:  CASI
    Details
    Publication Date: 2019-07-11
    Description: Recent advances in modeling languages have made it feasible to formally specify and analyze the behavior of large system components. Synchronous data flow languages, such as Lustre, SCR, and RSML-e are particularly well suited to this task, and commercial versions of these tools such as SCADE and Simulink are growing in popularity among designers of safety critical systems, largely due to their ability to automatically generate code from the models. At the same time, advances in formal analysis tools have made it practical to formally verify important properties of these models to ensure that design defects are identified and corrected early in the lifecycle. This report describes how these tools have been applied to the ADGS-2100 Adaptive Display and Guidance Window Manager being developed by Rockwell Collins Inc. This work demonstrates how formal methods can be easily and cost-efficiently used to remove defects early in the design cycle.
    Keywords: Computer Programming and Software
    Type: NASA/CR-2006-213952
    Format: application/pdf
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  • 7
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    A Methodology for the Design and Verification of Globally Asynchronous/Locally Synchronous Architectures (2005)
    In:  CASI
    Details
    Publication Date: 2019-07-11
    Description: Recent advanced in model-checking have made it practical to formally verify the correctness of many complex synchronous systems (i.e., systems driven by a single clock). However, many computer systems are implemented by asynchronously composing several synchronous components, where each component has its own clock and these clocks are not synchronized. Formal verification of such Globally Asynchronous/Locally Synchronous (GA/LS) architectures is a much more difficult task. In this report, we describe a methodology for developing and reasoning about such systems. This approach allows a developer to start from an ideal system specification and refine it along two axes. Along one axis, the system can be refined one component at a time towards an implementation. Along the other axis, the behavior of the system can be relaxed to produce a more cost effective but still acceptable solution. We illustrate this process by applying it to the synchronization logic of a Dual Fight Guidance System, evolving the system from an ideal case in which the components do not fail and communicate synchronously to one in which the components can fail and communicate asynchronously. For each step, we show how the system requirements have to change if the system is to be implemented and prove that each implementation meets the revised system requirements through modelchecking.
    Keywords: Computer Programming and Software
    Type: NASA/CR-2005-213912
    Format: application/pdf
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