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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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386 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS2022

NASA Engineering and Safety Center Technical Bulletin No. 22-04: Uncertainty Quantification of Reduced Order Structural Dynamic Models

Uncertainty quantification (UQ) provides statistical bounds on prediction accuracy based on finite element model (FEM) uncertainty. An alternate method for UQ, called the Hybrid Parametric Variation (HPV) combines a parametric variation of the Hurty/Craig-Bampton (HCB) fixed-interface (FI) modal frequencies with a nonparametric variation (NPV) method. This provides a UQ method that can be traced to test data, which can be updated as additional data and improved correlated models become available.

Uncertainty Quantification↗
NASA NTRS2022

NASA Engineering and Safety Center Technical Bulletin No. 22-05: Launch Vehicle Flight Control Stability Margin Reduction Considerations

Launch vehicle ascent stability analyses typically rely on a combination of frequency and time domain analyses. Frequency domain analysis uses a sequence of high-fidelity linear models with constant parameters spanning the ascent trajectory. Complementary time domain analysis is performed using high-fidelity, nonlinear 6-DOF simulations. Analyses are typically dispersed to verify robustness to parameter variations by showing the vehicle meets frequency domain stability margin requirements and time domain performance metrics. This Technical Bulletin outlines standard stability margin best practices and provides recommendations for treatment of deviations from industry-standard launch vehicle stability margins due to vehicle flexibility, slosh dynamics, aerodynamics, other offending dynamics, or coupling thereof.

Launch Vehicle↗
NASA NTRS2023

NASA Engineering and Safety Center Technical Bulletin No. 23-01: Including Key Design Features in Safety-Critical Pyrotechnic Firing Circuits

Pyrotechnic systems often fall into a unique category in that inadvertent activation of these systems resulting from a fault and/or lack of safe margins can lead directly to loss of crew. For example, untimely activation of pyrotechnics used for a flight termination system could override an abort capability. Over the years, NASA and the military have learned lessons about safe pyrotechnic circuit design and test, many of which are codified. However, with NASA’s recent efforts to move toward a development model than leans more heavily on Commercial Partners these requirements have not always been directly levied on projects and in some cases been misinterpreted. This bulletin describes key safety features of pyrotechnic firing circuit design and provides rationale for inclusion of each feature.

Pyrotechnic Firing Curcuits↗
NASA NTRS2023

New Transient Finite Energy Shock Prediction Methodology

Shock prediction is one of the top loads and dynamics discipline technical challenges identified within NASA and industry programs and projects. The physics-based Transient Finite Energy (TFE) shock prediction methodology has been developed and compared favorably against test results. TFE can provide another approach to develop predictions of shock response spectra (SRS) for use in the analysis of structural margins.

NESC Technical Bulletin No. 23-03↗
NASA NTRS2019

90/95 POD Radiography Concern for COPVs and Metal Tank Welds

Radiographic inspections of welds in all-metal tanks and composite overwrapped pressure vessel (COPV) liners that are used to establish initial crack size in damage tolerance assessments are not as rigorous as previously understood. As a result, the 90/95 percent probability of detection (POD) requirements in S-080 1 and S-081 2 are not met when this inspection method is used. Development of new inspection methods will require about three years. During that time, additional review and assessment of the fracture margin may be needed to support waivers and provide a better understanding of weld cracking risk associated with an individual tank design.

90/95 POD Radiography Concern↗
NASA NTRS2012

Structural Analyses and Margins of Safety

There is an increasing reliance on modeling and simulation to verify, quantify, and certify designs of complex structures. The availability of a range of commercial modeling and simulations tools and packages with a variety of capabilities, in conjunction with increased computational resources, is allowing analysts to rapidly perform detailed analyses. However, care should be taken to understand specific tool limitations, assumptions, and boundary conditions as erroneous results can be generated without being recognized by the analysts. In addition, the reported margins of safety should be carefully interrogated to identify any false positive or negative margins and highlight any areas for structural concern.

Structural Analyses↗