Results for “parametric uncertainty” — Page 10

NASA NTRS2015

Exploring Life Support Architectures for Evolution of Deep Space Human Exploration

Life support system architectures for long duration space missions are often explored analytically in the human spaceflight community to find optimum solutions for mass, performance, and reliability. But in reality, many other constraints can guide the design when the life support system is examined within the context of an overall vehicle, as well as specific programmatic goals and needs. Between the end of the Constellation program and the development of the "Evolvable Mars Campaign", NASA explored a broad range of mission possibilities. Most of these missions will never be implemented but the lessons learned during these concept development phases may color and guide future analytical studies and eventual life support system architectures. This paper discusses several iterations of design studies from the life support system perspective to examine which requirements and assumptions, programmatic needs, or interfaces drive design. When doing early concept studies, many assumptions have to be made about technology and operations. Data can be pulled from a variety of sources depending on the study needs, including parametric models, historical data, new technologies, and even predictive analysis. In the end, assumptions must be made in the face of uncertainty. Some of these may introduce more risk as to whether the solution for the conceptual design study will still work when designs mature and data becomes available.

Anderson, Molly↗

NASA NTRS2015

Exploring Life Support Architectures for Evolution of Deep Space Human Exploration

Life support system architectures for long duration space missions are often explored analytically in the human spaceflight community to find optimum solutions for mass, performance, and reliability. But in reality, many other constraints can guide the design when the life support system is examined within the context of an overall vehicle, as well as specific programmatic goals and needs. Between the end of the Constellation program and the development of the "Evolvable Mars Campaign", NASA explored a broad range of mission possibilities. Most of these missions will never be implemented but the lessons learned during these concept development phases may color and guide future analytical studies and eventual life support system architectures. This paper discusses several iterations of design studies from the life support system perspective to examine which requirements and assumptions, programmatic needs, or interfaces drive design. When doing early concept studies, many assumptions have to be made about technology and operations. Data can be pulled from a variety of sources depending on the study needs, including parametric models, historical data, new technologies, and even predictive analysis. In the end, assumptions must be made in the face of uncertainty. Some of these may introduce more risk as to whether the solution for the conceptual design study will still work when designs mature and data becomes available.

Anderson, Molly S.↗

NASA NTRS2023

Modeling and Simulation of a Parallel Hybrid Electric Regional Aircraft for the Electrified Powertrain Flight Demonstration (EPFD) Program

This paper presents a parametric modeling and integrated aircraft sizing and synthesis approach for a charge depleting parallel hybrid electric architecture. The developed models are integrated within the baseline thin-haul and regional aircraft. In addition to the physical architecture, different modes of operation enabled by propulsion system electrification are also modeled parametrically. The modes of operation presented in this paper are the peak power shaving, climb power electric boost, in-flight battery recharging, and electric taxi. The sizing of the powertrain and the aircraft are performed within the multidisciplinary analysis and optimization environment, E-PASS. The consideration of the physical system and its operation together provides a holistic approach where the propulsion system and the airframe are designed under an optimized power and energy management strategy. The parametric nature of the work enables the design space exploration for electrification and lays the groundwork for future technology projection and uncertainty quantification studies. The developed capability is generic and can be applied on other aircraft classes. The work is done as part of the Electrified Powertrain Flight Demonstration program.

electrified powertrain flight demonstration↗

NASA NTRS2001

Launcher Systems Development Cost: Behavior, Uncertainty, Influences, Barriers and Strategies for Reduction

This paper will report on the activities of the IAA Launcher Systems Economics Working Group in preparations for its Launcher Systems Development Cost Behavior Study. The Study goals include: improve launcher system and other space system parametric cost analysis accuracy; improve launcher system and other space system cost analysis credibility; and provide launcher system and technology development program managers and other decisionmakers with useful information on development cost impacts of their decisions. The Working Group plans to explore at least the following five areas in the Study: define and explain development cost behavior terms and concepts for use in the Study; identify and quantify sources of development cost and cost estimating uncertainty; identify and quantify significant influences on development cost behavior; identify common barriers to development cost understanding and reduction; and recommend practical, realistic strategies to accomplish reductions in launcher system development cost.

Shaw, Eric J.↗

NASA NTRS1993

Probabilistic simulation of the human factor in structural reliability

A formal approach is described in an attempt to computationally simulate the probable ranges of uncertainties of the human factor in structural probabilistic assessments. A multi-factor interaction equation (MFIE) model has been adopted for this purpose. Human factors such as marital status, professional status, home life, job satisfaction, work load and health, are considered to demonstrate the concept. Parametric studies in conjunction with judgment are used to select reasonable values for the participating factors (primitive variables). Suitability of the MFIE in the subsequently probabilistic sensitivity studies are performed to assess the validity of the whole approach. Results obtained show that the uncertainties for no error range from five to thirty percent for the most optimistic case.

Chamis, C. C.↗

NASA NTRS1982

Calculation of radiation from argon shock layers

The accuracy of calculations of the radiation emissions from argon plasmas produced by the shock layers over blunt bodies is assessed. The existing theoretical and experimental spectroscopic data on argon are collated. A set of such data is selected for use in the radiative transfer calculations. Calculations are performed for the stagnation regions of the shock layers over laboratory-sized models using these data, and the results are compared with the existing experimental results obtained in a shock-tube. Through this comparison and a parametric study it is shown that radiative heat fluxes at the stagnation point in an argon environment can be calculated within an uncertainty of about 15%. It is shown also that radiative heat fluxes of the order of 100 kW/sq cm can be produced in the existing laboratory facilities.

Park, C.↗

NASA NTRS1995

Some constraints on acceleration mechanisms in the solar wind at polar latitudes

Observations of solar Lyman alpha have been interpreted as indicating that the polar mass flux density is lower than the equatorial average. This led Lallement et al (1986) to make a parametric study of solar wind acceleration, along the lines of earlier the Munro-Jackson study (1977), in which they concluded that uncertainties in the polar mass flux were large enough to be consistent with two extreme opposites: (1) a substantial energy supply beyond classical thermal conduction is required; or (2) classical thermal conduction is adequate to drive the flow. This ambiguity has been clarified by Ulysses observations of the polar outflow (Phillips et al, 1994). The polar mass flux density lies in the middle of the range studies by Lallement et al (1986), which suggests that extended heating is going on out to at least approximately 5 AU. Independent, purely energetic arguments can be made to estimate the required coronal source (electron) temperature that would be required to account for the observed energy flux density. An electron temperature of at least 2 x 10(exp 6) K would be required for the classical conduction flux density to be comparable to the total energy flux density; such a high temperature is thought to be unlikely in a coronal hole. These arguments strongly suggest that some extended heating or momentum transfer mechanism is required to drive the solar wind from the polar coronal hole. A number of mechanisms are discussed.

Barnes, A.↗

NASA NTRS1986

Cost Risk Analysis Based on Perception of the Engineering Process

In most cost estimating applications at the NASA Langley Research Center (LaRC), it is desirable to present predicted cost as a range of possible costs rather than a single predicted cost. A cost risk analysis generates a range of cost for a project and assigns a probability level to each cost value in the range. Constructing a cost risk curve requires a good estimate of the expected cost of a project. It must also include a good estimate of expected variance of the cost. Many cost risk analyses are based upon an expert's knowledge of the cost of similar projects in the past. In a common scenario, a manager or engineer, asked to estimate the cost of a project in his area of expertise, will gather historical cost data from a similar completed project. The cost of the completed project is adjusted using the perceived technical and economic differences between the two projects. This allows errors from at least three sources. The historical cost data may be in error by some unknown amount. The managers' evaluation of the new project and its similarity to the old project may be in error. The factors used to adjust the cost of the old project may not correctly reflect the differences. Some risk analyses are based on untested hypotheses about the form of the statistical distribution that underlies the distribution of possible cost. The usual problem is not just to come up with an estimate of the cost of a project, but to predict the range of values into which the cost may fall and with what level of confidence the prediction is made. Risk analysis techniques that assume the shape of the underlying cost distribution and derive the risk curve from a single estimate plus and minus some amount usually fail to take into account the actual magnitude of the uncertainty in cost due to technical factors in the project itself. This paper addresses a cost risk method that is based on parametric estimates of the technical factors involved in the project being costed. The engineering process parameters are elicited from the engineer/expert on the project and are based on that expert's technical knowledge. These are converted by a parametric cost model into a cost estimate. The method discussed makes no assumptions about the distribution underlying the distribution of possible costs, and is not tied to the analysis of previous projects, except through the expert calibrations performed by the parametric cost analyst.

Dean, Edwin B.↗

NASA NTRS1996

Parametric Robust Control and System Identification: Unified Approach

During the period of this support, a new control system design and analysis method has been studied. This approach deals with control systems containing uncertainties that are represented in terms of its transfer function parameters. Such a representation of the control system is common and many physical parameter variations fall into this type of uncertainty. Techniques developed here are capable of providing nonconservative analysis of such control systems with parameter variations. We have also developed techniques to deal with control systems when their state space representations are given rather than transfer functions. In this case, the plant parameters will appear as entries of state space matrices. Finally, a system modeling technique to construct such systems from the raw input - output frequency domain data has been developed.

Keel, L. H.↗

NASA NTRS1979

Unconventional nozzle tradeoff study

Plug cluster engine design, performance, weight, envelope, operational characteristics, development cost, and payload capability, were evaluated and comparisons were made with other space tug engine candidates using oxygen/hydrogen propellants. Parametric performance data were generated for existing developed or high technology thrust chambers clustered around a plug nozzle of very large diameter. The uncertainties in the performance prediction of plug cluster engines with large gaps between the modules (thrust chambers) were evaluated. The major uncertainty involves, the aerodynamics of the flow from discrete nozzles, and the lack of this flow to achieve the pressure ratio corresponding to the defined area ratio for a plug cluster. This uncertainty was reduced through a cluster design that consists of a plug contour that is formed from the cluster of high area ratio bell nozzles that have been scarfed. Light-weight, high area ratio, bell nozzles were achieved through the use of AGCarb (carbon-carbon cloth) nozzle extensions.

Obrien, C. J.↗

NASA NTRS1998

Wavelet Filtering to Reduce Conservatism in Aeroservoelastic Robust Stability Margins

Wavelet analysis for filtering and system identification was used to improve the estimation of aeroservoelastic stability margins. The conservatism of the robust stability margins was reduced with parametric and nonparametric time-frequency analysis of flight data in the model validation process. Nonparametric wavelet processing of data was used to reduce the effects of external desirableness and unmodeled dynamics. Parametric estimates of modal stability were also extracted using the wavelet transform. Computation of robust stability margins for stability boundary prediction depends on uncertainty descriptions derived from the data for model validation. F-18 high Alpha Research Vehicle aeroservoelastic flight test data demonstrated improved robust stability prediction by extension of the stability boundary beyond the flight regime.

Brenner, Marty↗

NASA NTRS1998

On-Line Robust Modal Stability Prediction using Wavelet Processing

Wavelet analysis for filtering and system identification has been used to improve the estimation of aeroservoelastic stability margins. The conservatism of the robust stability margins is reduced with parametric and nonparametric time- frequency analysis of flight data in the model validation process. Nonparametric wavelet processing of data is used to reduce the effects of external disturbances and unmodeled dynamics. Parametric estimates of modal stability are also extracted using the wavelet transform. Computation of robust stability margins for stability boundary prediction depends on uncertainty descriptions derived from the data for model validation. The F-18 High Alpha Research Vehicle aeroservoelastic flight test data demonstrates improved robust stability prediction by extension of the stability boundary beyond the flight regime. Guidelines and computation times are presented to show the efficiency and practical aspects of these procedures for on-line implementation. Feasibility of the method is shown for processing flight data from time- varying nonstationary test points.

Brenner, Martin J.↗

NASA NTRS1998

Robust Control Design via Linear Programming

This paper deals with the problem of synthesizing or designing a feedback controller of fixed dynamic order. The closed loop specifications considered here are given in terms of a target performance vector representing a desired set of closed loop transfer functions connecting various signals. In general these point targets are unattainable with a fixed order controller. By enlarging the target from a fixed point set to an interval set the solvability conditions with a fixed order controller are relaxed and a solution is more easily enabled. Results from the parametric robust control literature can be used to design the interval target family so that the performance deterioration is acceptable, even when plant uncertainty is present. It is shown that it is possible to devise a computationally simple linear programming approach that attempts to meet the desired closed loop specifications.

Keel, L. H.↗

NASA NTRS1992

Fuzzy learning under and about an unfamiliar fuzzy teacher

This study addresses the problem of optimal parametric learning in unfamiliar fuzzy environments. Prior studies in the domain of unfamiliar environments, which employed either crisp or fuzzy approaches to model the uncertainty or imperfectness of the learning environment, assumed that the training sample labels provided by the unfamiliar teacher were crisp, even if not perfect. Here, the more realistic problem of fuzzy learning under an unfamiliar teacher who provides only fuzzy (instead of crisp) labels, is tackled by expanding the previously defined fuzzy membership concepts to include an additional component representative of the fuzziness of the teacher. The previously studied scenarios, namely, crisp and fuzzy learning under (crisp) unfamiliar teacher, can be looked upon as special cases of this new methodology. As under the earlier studies, the estimated membership functions can then be deployed during the ensuing classification decision phase to judiciously take into account the imperfectness of the learning environment. The study also offers some insight into the properties of several of these fuzzy membership function estimators by examining their behavior under certain specific scenarios.

Dasarathy, Belur V.↗

NASA NTRS2021

Parametric Study of State-of-Charge for an Electric Aircraft in Urban Air Mobility

The envisioned concept of urban air mobility is anticipated to support passenger transportation, cargo delivery, and emergency services in major metropolitan areas with increasing autonomy levels in the future. Distributed electric propulsion powered electric vertical takeoff and landing aircraft are expected to enable urban air mobility. However, the low specific energy of onboard lithium-ion polymer batteries and wind conditions impose constraints on flight endurance. Therefore, to enable autonomous urban air mobility operations using electric aircraft, one of the critical steps from a safety and efficiency perspective is to understand how various operational and environmental conditions impact the state-of-charge of the onboard lithium-ion polymer batteries. This research performs a parametric study of the state-of-charge for a NASA-proposed conceptual multirotor aircraft flight in the urban environment. The parameters considered for the parametric analysis are cruise airspeed, cruise altitude, climb and descent profiles, wind conditions (wind magnitude, wind direction relative to the route, and wind magnitude uncertainty), and required time of arrival.

Urban Air Mobility↗

NASA NTRS2021

Parametric Study of State of Charge for an Electric Aircraft in Urban Air Mobility

The envisioned concept of urban air mobility is anticipated to support passenger transportation, cargo delivery, and emergency services in major metropolitan areas with increasing autonomy levels in the future. Distributed electric propulsion powered electric vertical takeoff and landing aircraft are expected to enable urban air mobility. However, the low specific energy of onboard lithium-ion polymer batteries and wind conditions impose constraints on flight endurance. Therefore, to enable autonomous urban air mobility operations using electric aircraft, one of the critical steps from a safety and efficiency perspective is to understand how various operational and environmental conditions impact the state-of-charge of the onboard lithium-ion polymer batteries. This research performs a parametric study of the state-of-charge for a NASA-proposed conceptual multirotor aircraft flight in the urban environment. The parameters considered for the parametric analysis are cruise airspeed, cruise altitude, climb and descent profiles, wind conditions (wind magnitude, wind direction relative to the route, and wind magnitude uncertainty), and required time of arrival.

Urban Air Mobility↗

NASA NTRS2019

Orbit determination sensitivity analysis for th Europa Clipper Mission tour

This paper will assess the sensitivity of OD delivery and knowledge performance for the current Europa Mission trajectory through parametric variation of a baseline tour navigation strategy.2 Variations of several parameters are run, one at a time, to determine the impact on spacecraft ephemeris uncertainties at OD knowledge, delivery, and encounter reconstruction times. There are two basic categories of sensitivity runs considered: variations of tracking data type and amount, and variations to dynamic parameters. The results of these parameter and data variations are compared against the values necessary to achieve accurate instrument pointing and observation planning.

Young, Brian↗

NASA NTRS1982

On the statistical uncertainties associated with line profile fitting

The paper considers the statistical uncertainties in the best-fit parameters associated with the fitting of observational data by model line profiles of specific form. The parameters involved are amplitude, center, and width. A general procedure is described for any profile type of parametric form. The case of Gaussian profiles is treated in detail, and numerical solutions are presented for equally spaced data of equal weight. Approximate analytical solutions are derived that give good general agreement with the numerical solutions over the whole range of interest. Approximate solutions are also obtained for the case of Lorentzian profiles. It is shown that the Lorentzian results can be used in conjunction with the Gaussian results to estimate the corresponding parameter uncertainties in the case of the general Voigt profile.

Landman, D. A.↗