DATAWorks Sessions Archive

Statistical tolerance intervals of the form (1−α, P) provide bounds to capture at least a specified proportion P of the sampled population with a given confidence level 1−α. The quantity P is called the content of the tolerance interval and the confidence level 1−α reflects the sampling variability. Statistical tolerance intervals are ubiquitous in regulatory documents, especially regarding design verification and process validation. Examples of such regulations are those published by the Food and Drug Administration (FDA), the Environmental Protection Agency (EPA), the International Atomic Energy Agency (IAEA), and the standard 16269-6 of the International Organization for Standardization (ISO). Research and development in the area of statistical tolerance intervals has undoubtedly been guided by the needs and demands of industry experts. Some of the broad applications of tolerance intervals include their use in quality control of drug products, setting process validation acceptance criteria, establishing sample sizes for process validation, assessing biosimilarity, and establishing statistically-based design limits. While tolerance intervals are available for numerous parametric distributions, procedures are also available for regression models, mixed-effects models, and multivariate settings (i.e., tolerance regions). Alternatively, nonparametric procedures can be employed when assumptions of a particular parametric model are not met. Tools for computing such tolerance intervals and regions are a necessity for researchers and practitioners alike. This was the motivation for designing the R package ‘tolerance,’ which not only has the capability of computing a wide range of tolerance intervals and regions for both standard and non-standard settings, but also includes some supplementary visualization tools. This session will provide a high-level introduction to the ‘tolerance’ package and its many features. Relevant data examples will be integrated with the computing demonstration, and specifically designed to engage researchers and practitioners from industry and government. A recently-launched Shiny app corresponding to the package will also be highlighted.

The performance and reliability of additively manufactured (AM) metals is limited by the ubiquitous presence of void- and crack-like defects that form during processing. Many applications require non-destructive evaluation of AM metals to detect potentially critical flaws. To this end, we propose a deep learning approach that can help with the interpretation of inspection reports. Convolutional neural networks (CNN) are developed to predict the elastic stress fields in images of defect-containing metal microstructures, and therefore directly identify critical defects. A large dataset consisting of the stress response of 100,000 random microstructure images is generated using high-resolution Fast Fourier Transform-based finite element (FFT-FE) calculations, which is then used to train a modified U-Net style CNN model. The trained U-Net model more accurately predicted the stress response compared to previous CNN architectures, exceeded the accuracy of low-resolution FFT-FE calculations, and were evaluated more than 100 times faster than conventional FE techniques. The model was applied to images of real AM microstructures with severe lack of fusion defects, and predicted a strong linear increase of maximum stress as a function of pore fraction. This work shows that CNNs can aid the rapid and accurate inspection of defect-containing AM material.

Enabling Enhanced Validation of NDE Computational Models and Simulations William C. Schneck, III, Ph.D. Elizabeth D. Gregory, Ph.D. NASA Langley Research Center Computer simulations of physical processes are increasingly used in the development, design, deployment, and life-cycle maintenance of many engineering systems [1] [2]. Non-Destructive Evaluation (NDE) and Structural Health Monitoring (SHM) must employ effective methods to inspect increasingly complex structural and material systems developed for new aerospace systems. Reliably and comprehensively interrogating this multidimensional [3] problem domain from a purely experimental perspective can become cost and time prohibitive. The emerging way to confront these new complexities in a timely and cost-effective manner is to utilize computer simulations. These simulations must be Verified and Validated [4] [5] to assure reliable use for these NDE/SHM applications. Beyond the classical use of models for engineering applications for equipment or system design efforts, NDE/SHM are necessarily applied to as-built and as-used equipment. While most structural or CFD models are applied to ascertain performance of as-designed systems, the performance of an NDE/SHM system is necessarily tied to the indications of damage/defects/deviations (collectively, flaws) within as-built and as-used structures and components. Therefore, the models must have sufficient fidelity to determine the influence of these aberrations on the measurements collected during interrogation. To assess the accuracy of these models, the Validation data sets must adequately encompass these flaw states. Due to the extensive parametric spaces that this coverage would entail, this talk proposes an NDE Benchmark Validation Data Repository, which should contain inspection data covering representative structures and flaws. This data can be reused from project to project, amortizing the cost of performing high quality Validation testing. Works Cited [1] Director, Modeling and Simulation Coordination Office, “Department of Defense Standard Practice: Documentation of Verification, Validation, and Accredation (VV&A) for Models and Simulations,” Department of Defense, 2008. [2] Under Secretary of Defense (Acquisition, Technology and Logistics), “DoD Modeling and Simulation (M&S) Verification, Validation, and Accredation (VV&A),” Department of Defense, 2003. [3] R. C. Martin, Clean Architecture: A Craftsman’s Guide to Software Structure and Design, Boston: Prentice Hall, 2018. [4] C. J. Roy and W. L. Oberkampf, “A Complete Framework for Verification, Validation, and Uncertainty Quantification in Scientific Computing (Invited),” in 48th AIAA Aerospace Sciences Meeting, Orlando, 2010. [5] ASME Performance Test Code Committee 60, “Guide for Verification and Validation in Computational Solid Mechanics,” ASME International, New York, 2016.

This presentation outlines the design of experiments approach and data visualization techniques for a simulation study of sonic booms from NASA’s X-59 supersonic aircraft. The X-59 will soon be flown over communities across the contiguous USA as it produces a low-loudness sonic boom, or low-boom. Survey data on human perception of low-booms will be collected to support development of potential future commercial supersonic aircraft noise regulatory standards. The macroscopic atmosphere plays a critical role in the loudness of sonic booms. The extensive sonic boom simulation study presented herein was completed to assess climatological, geographical, and seasonal effects on the variability of the X-59’s low-boom loudness and noise exposure region size in order to inform X-59 community test planning. The loudness and extent of the noise exposure region make up the “sonic boom carpet.” Two spatial and temporal resolutions of atmospheric input data to the simulation were investigated. A Fast Flexible Space-Filling Design was used to select the locations across the USA for the two spatial resolutions. Analysis of simulated X-59 low-boom loudness data within a regional subset of the northeast USA was completed using a bootstrap forest to determine the final spatial and temporal resolution of the countrywide simulation study. Atmospheric profiles from NOAA’s Climate Forecast System Version 2 database were used to generate over one million simulated X-59 carpets at the final selected 138 locations across the USA. Effects of aircraft heading, season, geography, and climate zone on low-boom levels and noise exposure region size were analyzed. Models were developed to estimate loudness metrics throughout the USA for X-59 supersonic cruise overflight, and results were visualized on maps to show geographical and seasonal trends. These results inform regulators and mission planners on expected variations in boom levels and carpet extent from atmospheric variations. Understanding potential carpet variability is important when planning community noise surveys using the X-59.

The Department of Defense (DoD) has a considerable interest in forecasting key quantities of interest including demand signals, personnel flows, and equipment failure. Many forecasting tools exist to aid in predicting future outcomes, and there are many methods to evaluate the quality and uncertainty in those forecasts. When used appropriately, these methods can facilitate planning and lead to dramatic reductions in costs. This talk explores the application of machine learning algorithms, specifically gradient-boosted tree models, to forecasting and presents some of the various advantages and pitfalls of this approach. We conclude with an example where we use gradient-boosted trees to forecast Air National Guard personnel retention.

The DOD has to maintain readiness across a staggeringly diverse array of modern weapon systems, yet no single person or organization in the DOD has an end-to-end picture of the sustainment system that supports them. This shortcoming can lead to bad decisions when it comes to allocating resources in a funding-constrained environment. The underlying problem is driven by stovepiped databases, a reluctance to share data even internally, and a reliance on tribal knowledge of often cryptic data sources. Notwithstanding these difficulties, we need to create a comprehensive picture of the sustainment system to be able to answer pressing questions from DOD leaders. To that end, we have created a documented and reproducible workflow that shepherds raw data from DOD databases through cleaning and curation steps, and then applies logical rules, filters, and assumptions to transform the raw data into concrete values and useful metrics. This process gives us accurate, up-to-date data that we use to support quick-turn studies, and to rapidly build (and efficiently maintain) a suite of readiness models for a wide range of complex weapon systems.

Boolean responses are common for both tangible and simulation experiments. Well known approaches to fit models to Boolean responses include ordinary regression with normal approximations or variance stabilizing transforms, and logistic regression. Less well known is kernel regression. This session will present properties of kernel regression, its application to Bernoulli trial experiments, and other lessons learned from using kernel regression in the wild. Kernel regression is a non-parametric method. This requires modifications to many analyses, such as the required sample size. Unlike ordinary regression, the experiment design and model solution interact with each other. Consequently, the number of experiment samples for a desired modeling accuracy depends on the true state of nature. There has been trend in increasingly large simulation sample sizes as computing horsepower has grown. With kernel regression there is a point of diminishing return on sample sizes. That is, an experiment is better off with more data sites once a sufficient sample size is reached. Confidence interval accuracy is also dependent on the true state of nature. Parsimonious model tuning is required for accurate confidence intervals. Kernel tuning to build a parsimonious model using cross validation methods will be illustrated.

Machine learning algorithms can help to distill vast quantities of information to support decision making. However, machine learning also presents unique legal, moral, and ethical concerns – ranging from potential discrimination in personnel applications to misclassifying targets on the battlefield. Building on foundational principles in ethical philosophy, this presentation summarizes key legal, moral, and ethical criteria applicable to machine learning and provides pragmatic considerations and recommendations.

For AI-enabled and autonomous systems, issues of safety, security, and mission effectiveness are not separable—the same underlying data and software give rise to interrelated risks in all of these dimensions. If treated separately, there is considerable unnecessary duplication (and sometimes mutual interference) among efforts needed to satisfy commanders, operators, and certification authorities of the systems’ dependability. Assurances cases, pioneered within the safety and cybersecurity communities, provide a structured approach to simultaneously verifying all dimensions of system dependability with minimal redundancy of effort. In doing so, they also provide a more concrete and useful framework for system development and explanation of behavior than is generally seen in discussions of “transparency” and “trust” in AI and autonomy. Importantly, trust generally cannot be “built in” to systems, because the nature of the assurance arguments needed for various stakeholders requires iterative identification of evidence structures that cannot be anticipated by developers.

The DoD’s challenge to provide test results at the “Speed of Relevance” has generated many new strategies to accelerate data collection, adjudication, and analysis. As a result, the Air Force Operational Test and Evaluation Center (AFOTEC), in conjunction with the Air Force Chief Data Office’s Visible, Accessible, Understandable, Linked and Trusted Data Platform (VAULT), is developing a Survey Application. This new cloud-based application will be deployable on any AFNET-connected computer or tablet and merges a variety of tools for collection, storage, analytics, and decision-making into one easy-to-use platform. By placing cloud-computing power in the hands of operators and testers, authorized users can view report-quality visuals and statistical analyses the moment a survey is submitted. Because the data is stored in the cloud, demanding computations such as machine learning are run at the data source to provide even more insight into both quantitative and qualitative metrics. The T-7A Red Hawk will be the first operational test (OT) program to utilize the Survey Application. Over 1000 flying and simulator test points have been loaded into the application, with many more coming from developmental test partners. The Survey app development will continue as USAF testing commences. Future efforts will focus on making the Survey Application configurable to other research and test programs to enhance their analytic and reporting capabilities.

Sustainment for weapon systems involves multiple components that influence readiness outcomes through a complex array of interactions. While military leadership can use simple analytical approaches to yield insights into current metrics (e.g., dashboard for top downtime drivers) or historical trends of a given sustainment structure (e.g., correlative studies between stock sizes and backorders), they are inadequate tools for guiding decision-making due to their inability to quantify the impact on readiness. In this talk, we discuss the power of IDA’s end-to-end modeling and simulation (M&S) approach that estimates time-varying readiness outcomes based on real-world data on operations, supply, and maintenance. These models are designed to faithfully emulate fleet operations at the level of individual components and operational units, as well as to incorporate the multi-echelon inventory system used in military sustainment. We showcase a notional example in which our M&S approach produces a set of recommended component-level investments and divestments in wholesale supply that would improve the readiness of a weapon system. We argue for the urgency of increased end-to-end M&S efforts across the Department of Defense to guide the senior leadership in its data-driven decision-making for readiness initiatives.

Adopting uncertainty quantification (UQ) has become a prerequisite for providing credibility in modeling and simulation (M&S) applications. It is well known, however, that UQ can be computationally prohibitive for problems involving expensive high-fidelity models, since a large number of model evaluations is typically required. A common approach for improving efficiency is to replace the original model with an approximate surrogate model (i.e., metamodel, response surface, etc.) using machine learning that makes predictions in a fraction of the time. While surrogate modeling has been commonplace in the UQ field for over a decade, many practitioners still remain hesitant to rely on “black box” machine learning models over trusted physics-based models (e.g., FEA) for their analyses. This talk discusses the role of machine learning in enabling computational speedup for UQ, including traditional limitations and modern efforts to overcome them. An overview of surrogate modeling and its best practices for effective use is first provided. Then, some emerging methods that aim to unify physics-based and data-based approaches for UQ are introduced, including multi-model Monte Carlo simulation and physics-informed machine learning. The use of both traditional surrogate modeling and these more advanced machine learning methods for UQ are highlighted in the context of applications at NASA, including trajectory simulation and spacesuit certification.

Effective training of the broad set of users/operators of systems has downstream impacts on usability, workload, and ultimate system performance that are related to mission success. In order to measure training effectiveness, we designed a survey called the Operational Assessment of Training Scale (OATS) in partnership with the Army Test and Evaluation Center (ATEC). Two subscales were designed to assess the degrees to which training covered relevant content for real operations (Relevance subscale) and enabled self-rated ability to interact with systems effectively after training (Efficacy subscale). The full list of 15 items were given to over 700 users/operators across a range of military systems and test events (comprising both developmental and operational testing phases). Systems included vehicles, aircraft, C3 systems, and dismounted squad equipment, among other types. We evaluated reliability of the factor structure across these military samples using confirmatory factor analysis. We confirmed that OATS exhibited a two-factor structure for training relevance and training efficacy. Additionally, a shortened, six-item measure of the OATS with three items per subscale continues to fit observed data well, allowing for quicker assessments of training. We discuss various ways that the OATS can be applied to one-off, multi-day, multi-event, and other types of training events. Additional OATS details and information about other scales for test and evaluation are available at the Institute for Defense Analyses’ web site, https://testscience.org/validated-scales-repository/.

For analysis of military Developmental Test (DT) data, frequentist statistical models are increasingly challenged to meet the needs of analysts and decision-makers. Bayesian models have the potential to address this challenge. Although there is a substantial body of research on Bayesian reliability estimation, there appears to be a paucity of Bayesian applications to issues of direct interest to DT decision makers. To address this deficiency, this research accomplishes two tasks. First, this work provides a motivating example that analyzes reliability for a notional but representative system. Second, to enable the motivated analyst to apply Bayesian methods, it provides a foundation and best practices for Bayesian reliability analysis in DT. The first task is accomplished by applying Bayesian reliability assessment methods to notional DT lifetime data generated using a Bayesian reliability growth planning methodology (Wayne 2018). The tested system is assumed to be a generic complex system with a large number of failure modes. Starting from the Bayesian assessment methodology of (Wayne and Modarres, A Bayesian Model for Complex System Reliability 2015), this work explores the sensitivity of the Bayesian results to the choice of the prior distribution and compares the Bayesian results for the reliability point estimate and uncertainty interval with analogous results from traditional reliability assessment methods. The second task is accomplished by establishing a generic structure for systematically evaluating relevant statistical Bayesian models. It identifies what have been implicit reliability issues for DT programs using a structured poll of stakeholders combined with interviews of a selected set of Subject Matter Experts. Secondly, candidate solutions are identified in the literature. Thirdly, solutions matched to issues using criteria designed to evaluate the capability of a solution to improve support for decision-makers at critical points in DT programs. The matching process uses a model taxonomy structured according to decisions at each DT phase, plus criteria for model applicability and data availability. The end result is a generic structure that allows an analyst to identify and evaluate a specific model for use with a program and issue of interest. Wayne, Martin. 2018. “Modeling Uncertainty in Reliability Growth Plans.” 2018 Annual Reliability and Maintainability Symposium (RAMS). 1-6. Wayne, Martin, and Mohammad Modarres. 2015. “A Bayesian Model for Complex System Reliability.” IEEE Transactions on Reliability 64: 206-220.