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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 NTRS2012

Disruption of an Aligned Dendritic Network by Bubbles During Re-Melting in a Microgravity Environment

The quiescent Microgravity environment can be quite dynamic. Thermocapillary flow about "large" static bubbles on the order of 1mm in diameter was easily observed by following smaller tracer bubbles. The bubble induced flow was seen to disrupt a large dendritic array, effectively distributing free branches about the solid-liquid interface. "Small" dynamic bubbles were observed to travel at fast velocities through the mushy zone with the implication of bringing/detaching/redistributing dendrite arm fragments at the solid-liquid interface. Large and small bubbles effectively re-orient/re-distribute dendrite branches/arms/fragments at the solid liquid interface. Subsequent initiation of controlled directional solidification results in growth of dendrites having random orientations which significantly compromises the desired science.

Grugel, Richard N.↗
NASA NTRS2013

Bubble Induced Disruption of a Planar Solid-Liquid Interface During Controlled Directional Solidification in a Microgravity Environment

Pore Formation and Mobility Investigation (PFMI) experiments were conducted in the microgravity environment aboard the International Space Station with the intent of better understanding the role entrained porosity/bubbles play during controlled directional solidification. The planar interface in a slowing growing succinonitrile - 0.24 wt% water alloy was being observed when a nitrogen bubble traversed the mushy zone and remained at the solid-liquid interface. Breakdown of the interface to shallow cells subsequently occurred, and was later evaluated using down-linked data from a nearby thermocouple. These results and other detrimental effects due to the presence of bubbles during solidification processing in a microgravity environment are presented and discussed.

Grugel, Richard N.↗
NASA NTRS2013

Male and Female Summer Interns in Engineering from 2007-2012

The purpose of this study was to ascertain the colleges and universities from which engineering interns were chosen for the Langley Aerospace Research Student Scholars (LARSS) internship program over a six year period. While the initial question was where the interns were from, information was also obtained on these colleges and universities' rankings with respect to female faculty in tenure/tenure-track positions as well as research expenditures according to the American Society for Engineering Education's (ASEE) 2012 Annual Report. The majority of interns were selected from 14 institutions. Eight of the institutions for female interns and 7 for male interns were also cited as having the largest percentages/numbers of female faculty according to ASEE data. In 10 of the 14 institutions for male interns and 9 of 14 for female interns, the institutions were cited as having some of the highest research expenditures. Last, data from ASEE's report on bachelor degrees awarded in 2011 was assessed with respect to the 21 institutions listed as having higher numbers of women in tenure/tenure-track positions. The majority of these institutions represented larger engineering programs with a sizeable number of engineering faculty. These 21institutions accounted for 24.4% of the total engineering bachelor degrees awarded in 2011, with 27.4% of all female and 23.8% of all male graduates in the U.S.

Hall, Cathy W.↗
NASA NTRS2013

Female and Male Interns and Their Mentors? Perception of Workforce Skill Development

Participants in this study were student interns and mentors taking part in the 2012, 10- week Langley Aerospace Research Student Scholars (LARSS) summer internship program in Hampton, Virginia. The study examined mentors and student interns' ratings of their preparedness in basic knowledge and skills. The study focused on three primary areas: 1) overall evaluation of knowledge and skills by mentors and interns; 2) male and female interns' perceptions of their own skills in these key areas; and 3) mentors' perceptions of their student interns' knowledge and skills in the same areas by gender. Overall mentors were more positive about their interns' improvement in 12 of 17 areas assessed than were the student interns. There were no significant gender differences in how mentors rated their male and female interns' abilities in these workforce skills, but there were four key areas where female interns rated their own abilities lower than did their male peers: analytical thinking, computational skills, computer skills and technical skills. Implications of these findings are discussed.

Hall, Cathy W.↗
NASA NTRS2018

Comparison of Performance Test Results to CFD and Structural Models of Non-Contacting Finger Seals

Performance tests of non-contacting finger seal designs were conducted at 300, 700, 922 K (70, 800 and 1200 F) at pressure differentials up to 517 kPa (75 psid) and surface speeds up to 366 m/s (1200 ft/s). Room temperature, static analysis of the seal was performed. A simplified CFD model was developed to examine pressure loads within the seal. Results from the CFD model were used as input to a finite element analysis model of a six-finger segment of the non-contacting finger seal. Examination of predicted deflections of individual components of the seal gives insight into the seal behavior. Wear patterns from testing verify the pattern of radial deflection. The models are used to predict maximum pressure differential capability of the seal and compared to experimental results. The CFD model slightly under-predicts the measured leakage flow factor, but has the same trend as the measured flow factor versus pressure differential.

Seals:Brush Seals↗
NASA NTRS2018

Differential Adaptive Stress Testing of Airborne Collision Avoidance Systems

The next-generation Airborne Collision Avoidance System (ACAS X) is currently being developed and tested to replace the Traffic Alert and Collision Avoidance System (TCAS) as the next international standard for collision avoidance. To validate the safety of the system, stress testing in simulation is one of several approaches for analyzing near mid-air collisions (NMACs). Understanding how NMACs can occur is important for characterizing risk and informingdevelopment of the system. Recently, adaptive stress testing (AST) has been proposed as a way to find the most likely path to a failure event. The simulation-based approach accelerates search by formulating stress testing as a sequential decision process then optimizing it using reinforcement learning. The approach has been successfully applied to stress test a prototype of ACAS Xin various simulated aircraft encounters. In some applications, we are not as interestedin the system's absolute performance as its performance relative to another system. Such situations arise, for example, during regression testing or when deciding whether a new system should replace an existing system. In our collision avoidance application, we are interested in finding cases where ACAS X fails but TCAS succeeds in resolving a conflict. Existing approaches do not provide an efficient means to perform this type of analysis. This paper extends the AST approach to differential analysis by searching two simulators simultaneously and maximizing the difference between their outcomes. We call this approach differential adaptive stress testing (DAST). We apply DAST to compare a prototype of ACAS X against TCAS and show examples of encounters found by the algorithm.

Lee, Ritchie↗
NASA NTRS2020

Switchable Wettability for Condensation Heat Transfer

Condensation proceeds as dropwise or filmwise depending on the wettability of the condensing surface. These two modes of condensation have disparate heat transfer coefficients, with dropwise often exceeding filmwise. This work reports a surface with switchable superhydrophilic to hydrophobic wetting behavior that can exhibit both modes of condensation. Relative to the highly-wetting state which yields filmwise condensation, the non-wetting state exhibits dropwise condensation and twice the heat transfer coefficient. Relevance to thermal management is additionally discussed.

Heat transfer↗
NASA NTRS1998

Compact Drilling and Sample System

The Compact Drilling and Sample System (CDSS) was developed to drill into terrestrial, cometary, and asteroid material in a sryogenic, vacuum environment in order to acquire subsurface samples.

cryo↗