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  • 1
    Publication Date: 2019-07-13
    Description: This paper describes the use of Smoothed Particle Hydrodynamics (SPH) to simulate the water flow from the rainbird nozzle system used in the sound suppression system during pad abort and nominal launch. The simulations help determine if water from rainbird nozzles will impinge on the rocket nozzles and other sensitive ground support elements.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: KSC-E-DAA-TN18736 , KSC-E-DAA-TN18727 , SciTech 2015; Jan 05, 2015 - Jan 09, 2015; Kissimmee, FL; United States
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  • 2
    Publication Date: 2019-07-13
    Description: This paper develops techniques for predicting the uncertainty range of an output variable given input-output data. These models are called Interval Predictor Models (IPM) because they yield an interval valued function of the input. This paper develops IPMs having a radial basis structure. This structure enables the formal description of (i) the uncertainty in the models parameters, (ii) the predicted output interval, and (iii) the probability that a future observation would fall in such an interval. In contrast to other metamodeling techniques, this probabilistic certi cate of correctness does not require making any assumptions on the structure of the mechanism from which data are drawn. Optimization-based strategies for calculating IPMs having minimal spread while containing all the data are developed. Constraints for bounding the minimum interval spread over the continuum of inputs, regulating the IPMs variation/oscillation, and centering its spread about a target point, are used to prevent data over tting. Furthermore, we develop an approach for using expert opinion during extrapolation. This metamodeling technique is illustrated using a radiation shielding application for space exploration. In this application, we use IPMs to describe the error incurred in predicting the ux of particles resulting from the interaction between a high-energy incident beam and a target.
    Keywords: Statistics and Probability; Space Radiation
    Type: NF1676L-21631 , AIAA SciTech; Jan 04, 2016 - Jan 08, 2016; San Diego, CA; United States
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  • 3
    Publication Date: 2019-07-13
    Description: This and a companion paper propose techniques for constructing parametric mathematical models describing key features of the distribution of an output variable given input-output data. By contrast to standard models, which yield a single output value at each value of the input, Random Predictors Models (RPMs) yield a random variable at each value of the input. Optimization-based strategies for calculating RPMs having a polynomial dependency on the input and a linear dependency on the parameters are proposed. These formulations yield RPMs having various levels of fidelity in which the mean and the variance of the model's parameters, thus of the predicted output, are prescribed. As such they encompass all RPMs conforming to these prescriptions. The RPMs are optimal in the sense that they yield the tightest predictions for which all (or, depending on the formulation, most) of the observations are less than a fixed number of standard deviations from the mean prediction. When the data satisfies mild stochastic assumptions, and the optimization problem(s) used to calculate the RPM is convex (or, when its solution coincides with the solution to an auxiliary convex problem), the model's reliability, which is the probability that a future observation would be within the predicted ranges, can be bounded tightly and rigorously.
    Keywords: Statistics and Probability
    Type: NF1676L-20686 , European Safety and Reliability Association; Sep 07, 2015 - Sep 10, 2015; Zurich; Switzerland
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  • 4
    Publication Date: 2019-07-13
    Description: This and a companion paper propose techniques for constructing parametric mathematical models describing key features of the distribution of an output variable given input-output data. By contrast to standard models, which yield a single output value at each value of the input, Random Predictors Models (RPMs) yield a random variable at each value of the input. Optimization-based strategies for calculating RPMs having a polynomial dependency on the input and a linear dependency on the parameters are proposed. These formulations yield RPMs having various levels of fidelity in which the mean, the variance, and the range of the model's parameter, thus of the output, are prescribed. As such they encompass all RPMs conforming to these prescriptions. The RPMs are optimal in the sense that they yield the tightest predictions for which all (or, depending on the formulation, most) of the observations are less than a fixed number of standard deviations from the mean prediction. When the data satisfies mild stochastic assumptions, and the optimization problem(s) used to calculate the RPM is convex (or, when its solution coincides with the solution to an auxiliary convex problem), the model's reliability, which is the probability that a future observation would be within the predicted ranges, is bounded rigorously.
    Keywords: Systems Analysis and Operations Research; Statistics and Probability
    Type: NF1676L-20687 , European Safety and Reliability Conference (ESREL 2015); Sep 07, 2015 - Sep 10, 2015; Zurich; Switzerland
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  • 5
    Publication Date: 2019-07-13
    Description: An interval predictor model (IPM) is a computational model that predicts the range of an output variable given input-output data. This paper proposes strategies for constructing IPMs based on semidefinite programming and sum of squares (SOS). The models are optimal in the sense that they yield an interval valued function of minimal spread containing all the observations. Two different scenarios are considered. The first one is applicable to situations where the data is measured precisely whereas the second one is applicable to data subject to known biases and measurement error. In the latter case, the IPMs are designed to fully contain regions in the input-output space where the data is expected to fall. Moreover, we propose a strategy for reducing the computational cost associated with generating IPMs as well as means to simulate them. Numerical examples illustrate the usage and performance of the proposed formulations.
    Keywords: Statistics and Probability; Mathematical and Computer Sciences (General)
    Type: NF1676L-25443 , 2017 American Control Conference; May 24, 2017 - May 26, 2017; Seattle, WA; United States
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  • 6
    Publication Date: 2019-07-13
    Description: This paper presents a comparative analysis of a few metamodeling techniques using numerical experiments for the single input-single output case. These experiments enable comparing the models' predictions with the phenomenon they are aiming to describe as more data is made available. These techniques include (i) prediction intervals associated with a least squares parameter estimate, (ii) Bayesian credible intervals, (iii) Gaussian process models, and (iv) interval predictor models. Aspects being compared are computational complexity, accuracy (i.e., the degree to which the resulting prediction conforms to the actual Data Generating Mechanism), reliability (i.e., the probability that new observations will fall inside the predicted interval), sensitivity to outliers, extrapolation properties, ease of use, and asymptotic behavior. The numerical experiments describe typical application scenarios that challenge the underlying assumptions supporting most metamodeling techniques.
    Keywords: Numerical Analysis; Statistics and Probability
    Type: NF1676L-21664 , AIAA SciTech Forum and Exposition; Jan 04, 2016 - Jan 08, 2016; San Diego, CA; United States
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  • 7
    Publication Date: 2019-07-13
    Description: The Advanced Radiation Protection Thick Galactic Cosmic Ray (GCR) Shielding Project leverages experimental and modeling approaches to validate a predicted minimum in the radiation exposure versus shielding depth curve. Preliminary results of space radiation models indicate that a minimum in the dose equivalent versus aluminum shielding thickness may exist in the 20-30 g/cm2 region. For greater shield thickness, dose equivalent increases due to secondary neutron and light particle production. This result goes against the long held belief in the space radiation shielding community that increasing shielding thickness will decrease risk to crew health. A comprehensive modeling effort was undertaken to verify the preliminary modeling results using multiple Monte Carlo and deterministic space radiation transport codes. These results verified the preliminary findings of a minimum and helped drive the design of the experimental component of the project. In first-of-their-kind experiments performed at the NASA Space Radiation Laboratory, neutrons and light ions were measured between large thicknesses of aluminum shielding. Both an upstream and a downstream shield were incorporated into the experiment to represent the radiation environment inside a spacecraft. These measurements are used to validate the Monte Carlo codes and derive uncertainty distributions for exposure estimates behind thick shielding similar to that provided by spacecraft on a Mars mission. Preliminary results for all aspects of the project will be presented.
    Keywords: Space Radiation; Spacecraft Design, Testing and Performance
    Type: NF1676L-27179 , Applied Space Environments Conference (ASEC) 2017; May 15, 2017 - May 19, 2017; Huntsville, AL; United States
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  • 8
    Publication Date: 2019-07-12
    Description: This paper reports on the formalization of a recent result by Crespo, et al., as found in the references. The formalized result bounds the number of support constraints in a particular type of optimization problem. The problem involves discovering an optimal member of a family of sets that overlaps each member of a constraining collection of sets. The particular case addressed here concerns optimizations in which the family of sets is nested. The primary results were formalized in the interactive theorem prover PVS and support the claim that a single support constraint exists in very general circumstances.
    Keywords: Numerical Analysis
    Type: NASA/TM-2018-220117 , L-20973 , NF1676L-31613
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  • 9
    Publication Date: 2019-07-13
    Description: This paper presents a framework for calibrating computational models using data from several and possibly dissimilar validation experiments. The offset between model predictions and observations, which might be caused by measurement noise, model-form uncertainty, and numerical error, drives the process by which uncertainty in the models parameters is characterized. The resulting description of uncertainty along with the computational model constitute a predictor model. Two types of predictor models are studied: Interval Predictor Models (IPMs) and Random Predictor Models (RPMs). IPMs use sets to characterize uncertainty, whereas RPMs use random vectors. The propagation of a set through a model makes the response an interval valued function of the state, whereas the propagation of a random vector yields a random process. Optimization-based strategies for calculating both types of predictor models are proposed. Whereas the formulations used to calculate IPMs target solutions leading to the interval value function of minimal spread containing all observations, those for RPMs seek to maximize the models' ability to reproduce the distribution of observations. Regarding RPMs, we choose a structure for the random vector (i.e., the assignment of probability to points in the parameter space) solely dependent on the prediction error. As such, the probabilistic description of uncertainty is not a subjective assignment of belief, nor is it expected to asymptotically converge to a fixed value, but instead it casts the model's ability to reproduce the experimental data. This framework enables evaluating the spread and distribution of the predicted response of target applications depending on the same parameters beyond the validation domain.
    Keywords: Systems Analysis and Operations Research; Statistics and Probability
    Type: NF1676L-18985 , AIAA Aerospace Sciences Meeting (SciTech 2015); Jan 05, 2015 - Jan 09, 2015; Kissimmee, FL; United States
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  • 10
    Publication Date: 2019-11-19
    Description: This paper proposes techniques for constructing non-parametric computational models describing the distribution of a continuous output variable given input-output data. These models are called Random Predictor Models (RPMs) because the predicted output corresponding to any given input is a random variable. One common example of an RPM is a Gaussian process (GP) model. In contrast to GP models however, we focus on RPMs having a bounded support set and prescribed values for the mean, and the second-, third-, and fourth-order central moments. The proposed RPMs are designed to match moment functions extracted from the data over a range of minimal spread. This paper presents the feasibility conditions that any random variable must meet in order to satisfy the desired constraints. Furthermore, a particular family of such variables, called staircase because their probability density is a piecewise constant function, is proposed. The ability of these variables to describe a wide range of probability density shapes, and their low computational cost enable the efficient generation of possibly skewed and multimodal RPMs over an input-dependent interval.
    Keywords: Numerical Analysis
    Type: NF1676L-26266 , Applied Mathematical Modelling (ISSN 0307-904X); 64; 196-213
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