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NASA NTRS1981

A comparison of in-cloud HCl concentrations from the NASA/MSFC MDM to measurements for the space shuttle launch

The Multilevel Diffusion Model (MDM) Version 5 was modified to include features of more recent versions. The MDM was used to predict in-cloud HCl concentrations for the April 12 launch of the space Shuttle (STS-1). The maximum centerline predictions were compared with measurements of maximum gaseous HCl obtained from aircraft passes through two segments of the fragmented shuttle ground cloud. The model over-predicted the maximum values for gaseous HCl in the lower cloud segment and portrayed the same rate of decay with time as the observed values. However, the decay with time of HCl maximum predicted by the MDM was more rapid than the observed decay for the higher cloud segment, causing the model to under-predict concentrations which were measured late in the life of the cloud. The causes of the tendency for the MDM to be conservative in over-estimating the HCl concentrations in the one case while tending to under-predict concentrations in the other case are discussed.

Glasser, M. E.↗

NASA NTRS1988

Integrating causal reasoning at different levels of abstraction

In this paper, a problem-solving system which uses a multilevel causal model of its domain is described. The system functions in the role of a pilot's assistant in the domain of commercial air transport emergencies. The model represents causal relationships among the aircraft subsystems, the effectors (engines, control surfaces), the forces that act on an aircraft in flight (thrust, lift), and the aircraft's flight profile (speed, altitude, etc.). The causal relationships are represented at three levels of abstraction: Boolean, qualitative, and quantitative, and reasoning about causes and effects can take place at each of these levels. Since processing at each level has different characteristics with respect to speed, the type of data required, and the specificity of the results, the problem-solving system can adapt to a wide variety of situations. The system is currently being implemented in the KEE(TM) development environment on a Symbolics Lisp machine.

Hudlicka, Eva↗

NASA NTRS1989

Probabilistic structural analysis of space propulsion system turbine blades

Probabilistic loads and stress analysis methods are presently applied to the second-stage blade of the SSME's high-pressure fuel turbopump, in order to illustrate how loads and stress responses can be quantified probabilistically and how the sensitivity of such component- and engine-level independent variables as engine inlet temperatures and local seal wear within the turbopump can be determined. Attention is given to a method for the derivation of probabilistic pressure, temperature, and centrifugal steady-state load descriptions of this second-stage blade from the top of the airfoil to its intersection with the firtree. Dependent-load random variables are obtained from a multilevel physical model in which duty cycle-dependent deterministic loads and related probabilistic variations are accounted for.

Newell, J. F.↗

NASA NTRS1989

UNIX security in a supercomputing environment

The author critiques some security mechanisms in most versions of the Unix operating system and suggests more effective tools that either have working prototypes or have been implemented, for example in secure Unix systems. Although no computer (not even a secure one) is impenetrable, breaking into systems with these alternate mechanisms will cost more, require more skill, and be more easily detected than penetrations of systems without these mechanisms. The mechanisms described fall into four classes (with considerable overlap). User authentication at the local host affirms the identity of the person using the computer. The principle of least privilege dictates that properly authenticated users should have rights precisely sufficient to perform their tasks, and system administration functions should be compartmentalized; to this end, access control lists or capabilities should either replace or augment the default Unix protection system, and mandatory access controls implementing multilevel security models and integrity mechanisms should be available. Since most users access supercomputing environments using networks, the third class of mechanisms augments authentication (where feasible). As no security is perfect, the fourth class of mechanism logs events that may indicate possible security violations; this will allow the reconstruction of a successful penetration (if discovered), or possibly the detection of an attempted penetration.

Bishop, Matt↗

NASA NTRS2001

Effects of Normal Aging on Visuo-Motor Plasticity

Normal aging is associated with declines in neurologic function. Uncompensated visual and vestibular problems may have dire consequences including dangerous falls. Visuomotor plasticity is a form of behavioral neural plasticity which is important in the process of adapting to visual or vestibular alteration, including those changes due to pathology, pharmacotherapy, surgery or even entry into a microgravity or underwater environment. In order to determine the effects of aging on visuomotor plasticity, we chose the simple and easily measured paradigm of visual-motor re-arrangement created by using visual displacement prisms while throwing small balls at a target. Subjects threw balls before, during and after wearing a set of prisms which displace the visual scene by twenty degrees to the right. Data obtained during adaptation were modeled using multilevel analyses for 73 subjects aged 20 to 80 years. We found no statistically significant difference in measures of visuomotor plasticity with advancing age. Further studies are underway examining variable practice training as a potential mechanism for enhancing this form of behavioral neural plasticity.

Roller, Carrie A.↗

NASA NTRS2025

Measuring Unique Contextual Factors: Group Living Skills

BACKGROUND The Human Factors and Behavioral Performance Exploration Measures (HFBP-EM) suite is a set of standardized measures used to assess behavioral health and performance risks related to future exploration-class space missions. During the HFBP-EM suite development, the importance of assessing unique contextual factors to understand the drivers of team dynamics was identified. Group living skills are a unique workplace skill which applies to those coworkers who live and work together. As mission lengths become longer, the line between work and non-work life may blur. Extreme living conditions such as spaceflight can result in increased stress over time, negatively impact mood and well-being, decrease team cohesion and increase conflict, deteriorate task performance, and potentially reduce mission success [1]. With no breaks in their isolated and confined environment possible, living with a messy, inconsiderate crewmember can add to the stress. Alternatively, crews with good group living skills may support one another, mitigating the negative effects of the extreme environment. There was no direct measure of group living skills. This work sought to fill this measurement gap and collect data related to group living in isolated, confined, extreme (ICE) environments. METHODS Group living skills as an astronaut competency area were developed with the input of experts familiar with ICE environments. Distinct aspects of this competency were reviewed and discussed by a NASA-invited group of spaceflight experts in 2015 to identify individual and team behavioral health and performance measures for operational environments. This work resulted in a 5-item measure focused on group living experiences with each crewmember (or the crew as a whole). A 6th item asks whether an individual would go on another mission with a particular crewmember or crew as a measure of future-oriented group living, or team viability. The measure was deployed in 24 teams living and working together in isolated and confined environments (e.g., International Space Station, space mission simulation analogs). RESULTS & DISCUSSION In this presentation, we will summarize results which indicate the Group Living Skills (GLS) Survey is a reliable, valid, and operationally feasible measure. Reliability was evaluated in several ways. Two-way multilevel mixed models revealed strong repeated measures reliability (ICC2 = .902, Omega between = .954). Reliability of change within teams was strong (Rc = .81). Factor analysis showed a consistent two-factor structure when individuals rated either the whole crew, all individuals, just peers, or a focal roommate. The latter used a sociometric approach to rating the GLS of the roommates. The two factors were tidiness and being considerate of others. We assessed the criterion-related validity of GLS, by examining GLS operationalized as the team-level aggregated GLS Survey scores as a predictor of team viability, team cohesion, and team performance. We used generalized mixed models to account for the repeated measures and longitudinal data. The marginal R2 change was used to determine the extent to which GLS were related to the team outcomes while controlling for mission day and campaign. Results suggested GLS was strongly related to team viability (marginal R2 change = .40), team cohesion (marginal R2 change = 0.28), social cohesion (marginal R2 change = 0.25), and moderately related to task cohesion (marginal R2 change = 0.18). GLS scores had a small relationship with team performance (marginal R2 change = .08). Results support GLS as a measure that can be used to capture group living skills of crews who live and work together in ICE. Because the items were written to be broadly applicable, less extreme environments with teams living and working together for some length of time also benefit from this measure (e.g., college roommates, camps). See Landon et al. (2024) for full results [2]. SUMMARY We report reliability and validity evidence for a new measure that assesses the Group Living Skills for teams that live and work in operational environments such as spaceflight.

J C W Miller↗

NASA NTRS2026

Helicopter and Urban Air Mobility (UAM) Laboratory Comparison (HULC) Psychoacoustic Test

The Helicopter and Urban Air Mobility (UAM) Laboratory Comparison (HULC) psychoacoustic test was conducted in July 2025 to compare human annoyance responses to noise from UAM vehicles and helicopters. This document provides a literature review, describes the HULC test methodology including stimuli selection and test administration procedures, and presents results from an initial analysis using multilevel statistical modeling. The test utilized 123 sound stimuli from four helicopters and six UAM vehicles across three flight phases (departure, cruise, and approach), presented to 40 subjects in the Exterior Effects Room (EER) at NASA's Langley Research Center. Subjects rated their annoyance on a 0 to 10 scale while imagining hearing these sounds multiple times daily near their homes. Key findings revealed that, at the same A-weighted sound exposure levels, UAM vehicles and helicopters produced similar annoyance responses across all flight phases, with mean differences of only approximately 1 dB and overlapping confidence intervals. However, at equivalent observer distances, UAM vehicles had inherently quieter operations and lower mean annoyance ratings. These results suggest that UAM vehicles and helicopters may be assessed in a similar manner for community noise impact. The quieter noise characteristics of UAM vehicles may provide advantages for operating in communities and integrating into urban environments.

psychoacoustics↗

NASA NTRS1987

The effect of the Hadley circulation on the meridional propagation of stationary waves

The effect of the Hadley circulation on the meridional propagation of stationary planetary waves was investigated using a multilevel linearized steady primitive equation model with an idealized meridional circulation. It was found that a mean meridional circulation in the basic state can change the response of a multilevel model, especially to forcing in the tropics. The idealized model version was altered in several ways and was run with realistic zonal mean conditions of January and July for a variety of forcings, including topographic forcing and idealized tropical heating. In this model, the Hadley circulation changes the response to earth topographic forcing in the subtropics. The inclusion of the Hadley circulation allows interhemispheric connections in the stationary response to tropical forcing comparable to those that observations suggest are forced by the Asian monsoon in July and the anomalous upper-tropospheric divergence during the El Nino in January.

Watterson, Ian G.↗

DOE OSTI2020

A Simplified Model Predictive Control Strategy for a Nine-Level Hybrid Multilevel Converter

This paper proposes a simplified model predictive control (SMPC) for a 9-level hybrid multilevel converter based on the active-neutral-point-clamped (ANPC) topology. The proposed SMPC firstly identifies the voltage vector that has optimal current tracking performance by a novel geometrical positioning approach in the complex plane, which can dramatically reduce the computational burden. Then it evaluates the switching states that are subject to the same voltage vector and selects the optimal switching state to balance the dc capacitor voltages. Both simulation and experimental results are carried out to validate the feasibility and effectiveness of the proposed control strategy.

14 SOLAR ENERGY↗

DOE OSTI2020

A Virtual Space Vector Model Predictive Control for a Seven-Level Hybrid Multilevel Converter

This paper proposes a virtual space vector (VSV) model predictive control (MPC) for a three-phase seven-level (7L) hybrid multilevel converter (HMC), where each phase consists of an active-neutral-point-clamped converter with a floating H-bridge. To achieve the best current tracking, which is the primary goal of the proposed algorithm, a novel geometrical positioning approach is proposed to select the optimal voltage vector among all the realspace vectors and VSVs. Then, all the possible switching sequences that belong to the optimal voltage vector are evaluated to realize the dc capacitor voltage balancing and common-mode voltage reduction. Through an external modulator, the optimal voltage vector can be synthesized by using either one-, three-, or seven-segment switching sequence. Compared with the conventional MPC, the proposed VSV-MPC can reduce not only the computational burden but also the current THD. Both simulation and experimental results obtained on silicon carbide based 7L-HMC prototype are presented to validate the feasibility and effectiveness of the proposed VSVMPC strategy.

42 ENGINEERING↗

NASA NTRSDate not supplied

The effect of modeling dose uncertainty on low-boom community noise dose-response curves

In logistic dose-response modeling, failing to account for uncertainty in estimated doses can cause an artificial flattening or attenuation of the slope of the summary curve. In Lee et al. [J. Acoust. Soc. Am. 147(4), pp. 2222-2234 (2020)], data from two NASA low-amplitude sonic boom community noise survey tests were modeled using a Bayesian multilevel logistic regression (MLR) statistical model that assumed there was no uncertainty in the noise dose estimates. However, in these community tests, the noise dose uncertainty was estimated by Page et al. [NASA/CR-2014-218180 and NASA/CR-2020-220589/Volume I] using a leave-one-out method. In the current work, a term was added to extend the Bayesian MLR model to account for the estimated noise dose uncertainty quantified in the Page et al. analyses. This uncertainty term was included in two ways, either as classical or as Berkson uncertainty, and yield similar results. When the uncertainty is accounted for in the Bayesian MLR model, the dose-response curves become 5-10% steeper, but the difference in the noise dose that elicits a 5% highly annoyed response is small (less than 1 dB). This result is encouraging for future X-59 community tests whose survey area will be sparsely populated with noise monitors.

X-59↗

NASA NTRSDate not supplied

Modeling approaches to estimate community annoyance due to sonic booms using data from repeated surveys

In an on-going project for NASA, we are developing a modeling approach to analyze the relationship between the noise level of sonic booms from an experimental supersonic plane and the level of annoyance measured through community response surveys. The goal of the project is to obtain a quantitative relationship between noise level and annoyance that is representative for the affected population. Particular modeling challenges include multiple annoyance measurements per survey respondent and very few occurrences of annoyance overall. To address these challenges, we propose a two-stage model for the presence of high annoyance, with the first stage modeling the probability that a respondent is ever highly annoyed and the second stage a multilevel logistic regression model for high annoyance based on noise level and demographic characteristics. We use a variation of Multilevel Regression and Poststratification (Gelman and Little, 1997) to obtain an overall representative noise-annoyance curve for the population. The approach is applied to data from a NASA pilot study.

Robyn Ferg↗

NASA NTRSDate not supplied

Modeling Approaches to Estimate Community Annoyance Due to Sonic Booms Using Data from Repeated Surveys

Robyn Ferg↗

DOE OSTI2024

Modeling and ZVS Operation of the Isolated Modular Multilevel DC–DC Converter With a Unified Trapezoidal Wave Modulation

Here, this article introduces a unified trapezoidal wave (UTW) modulation scheme for the isolated modular multilevel dc–dc (IM2dc) converter, which consolidates multiple existing modulation strategies for the IM2dc converter, including the quasi-square wave (QSW) modulation, trapezoidal wave modulation, and sinusoidal wave modulation, into a unified framework. Furthermore, this article introduces the harmonic state-space (HSS) equations to model the IM2dc converter based on the UTW modulation method. The HSS model operates in the frequency domain, enabling it to circumvent the complexities associated with time-domain analysis and seamlessly integrate with the UTW modulation. This article proceeds to analyze the real and reactive power transfer characteristics of the IM2dc converter, as well as the power factor, considering the influence of multiple modulation parameters. Subsequently, it delves into the examination of zero voltage switching (ZVS) conditions for the IM2dc converter based on the UTW modulation and the HSS model. The complete ZVS boundaries of the IM2dc converter, taking various voltage ratios into account, are derived. This article also illustrates the effects of including harmonic orders in the modeling process, modulation parameters, and internal harmonic ripples on the ZVS boundaries. Finally, experimental validation of the analyses is conducted on a down-scaled prototype.

42 ENGINEERING↗

NASA NTRS2020

Bayesian Statistical Models for Community Annoyance Survey Data

This paper demonstrates the use of two Bayesian statistical models to analyze single-event sonic boom exposure and human annoyance data from community response surveys. Each model is fit to data from a NASA pilot study.Unlike many community noise surveys, this study used a panel sample to collect multiple observations per participant instead of a single observation. Thus, a multilevel (also known as hierarchical or mixed-effects) model is used to account for the within-subject correlation in the panel sample data. This paper describes a multilevel logistic regression model and a multilevel ordinal regression model. The paper also proposes a method for calculating a summary dose-response curve from the multilevel models that represents the population. The two models’ summary dose-response curves are visually similar. However, their estimates differ when calculating the noise dose at a fixed percent highly annoyed.

Musical instruments↗

NASA NTRS1999

Structured Course Objects in a Digital Library

We are developing an Undergraduate Digital Library Framework (UDLF) that will support creation/archiving of courses and reuse of existing course material to evolve courses. UDLF supports the publication of course materials for later instantiation for a specific offering and allows the addition of time-dependent and student-specific information and structures. Instructors and, depending on permissions, students can access the general course materials or the materials for a specific offering. We are building a reference implementation based on NCSTRL+, a digital library derived from NCSTRL. Digital objects in NCSTRL+ are called buckets, self-contained entities that carry their own methods for access and display. Current bucket implementations have a two level structure of packages and elements. This is not a rich enough structure for course objects in UDLF. Typically, courses can only be modeled as a multilevel hierarchy and among different courses, both the syntax and semantics of terms may vary. Therefore, we need a mechanism to define, within a particular library, course models, their constituent objects, and the associated semantics in a flexible, extensible way. In this paper, we describe our approach to define and implement these multilayered course objects. We use XML technology to emulate complex data structures within the NCSTRL+ buckets. We have developed authoring and browsing tools to manipulate these course objects. In our current implementation a user downloading an XML based course bucket also downloads the XML-aware tools: an applet that enables the user to edit or browse the bucket. We claim that XML provides an effective means to represent multi-level structure of a course bucket.

Maly, K.↗

NASA NTRS2022

Simulation and Application of Bayesian Dose Uncertainty Modeling for Low-Boom Community Noise Surveys

In dose-response modeling, failing to account for dose uncertainty can cause artificial flattening of the estimated slope of the dose-response curve. Previous analyses of NASA sonic boom community noise survey data utilized a Bayesian multilevel logistic regression model, which did not account for dose uncertainty. The current work extends the model to account for either classical or Berkson dose uncertainty. The extended model is applied to two simulated dose-response datasets to illustrate conditions under which the dose uncertainty term does and does not correct for the artificial flattening introduced by dose uncertainty. Finally, the extended model is applied to two previous NASA sonic boom community noise surveys. The resulting dose-response curve slope for the average participant is 5 to 10% steeper, but the difference in the noise dose that elicits a 5% highly annoyed response is small (less than 1 dB). The difference remains insignificant when producing population summary dose-response curves. Commentary is included on applicability to future X-59 low-boom community noise survey data modeling and analysis.

X-59↗

DOE OSTI2021

A Phase-Disposition PWM Enabled Model Predictive Control for a Nine-Level Inner-Interleaved Hybrid Multilevel Converter

This article brings forward a phase-disposition pulse width modulation enabled model predictive control (PDPWM-MPC) for a nine-level inner-interleaved hybrid multilevel converter (9L-IHMC). Firstly, three layers of virtual space vector diagrams (VSVD) are established based on the sign patterns of the original and virtual reference vectors in the abcframe, respectively, to achieve the phase-disposition pulse width modulation (PD-PWM) in a non-independent three-phase way. Then, three adjacent virtual vectors in the third-layer VSVD, together with their optimized duty cycles, are applied to guarantee the optimal current tracking. Finally, through the use of the duty cycle alternation approach, dc-link and floating capacitors voltages are balanced and circulating currents are mitigated as well. The proposed PDPWM-MPC can not only enable the decoupling of the low-and high-frequency stages in the 9L-IHMC, but also reduce both output current ripples and computational burden. In addition, it can achieve a constant equivalent switching frequency and address the disproportion of power losses associated with the PD-PWM. Here, both simulations and experiments on a silicon carbide device-based prototype substantiate the effectiveness of the proposed control strategy.

42 ENGINEERING↗