DATAWorks Sessions Archive

This paper presents the results of two hypervelocity impact failure probabilistic risk assessments for critical wire bundles exposed aboard the Joint Polar Satellite System (JPSS-1) to an increased orbital debris environment at its 824 km, 98.8 deg inclination orbit. The first “generic” approach predicted the number of wires broken by orbital debris ejecta emerging from normal impact with multi-layer insulation (MLI) covering 36-, 18-, and 6-strand wire bundles at a 5 cm standoff using the Smooth Particle Hydrodynamic (SPH) code. This approach also included a mathematical approach for computing the probability that redundant wires were impacted then severed within the bundle. Based in part on the high computed risk of a critical wire bundle failure from the generic approach, an enhanced orbital debris protection design was examined, consisting of betacloth-reinforced MLI suspended at a 5 cm standoff over a seven layer betacloth and Kevlar blanket, draped over the exposed wire bundles. A second SPH-based risk assessment was conducted that also included the beneficial effects from the high (75 degree) obliquity of orbital debris impact and shadowing by other spacecraft components, and resulted in a considerably reduced likelihood of critical wire bundle failure compared to the original baseline design.

For the past 7 years, USAF DT&E has been exploring ways to adapt the principles of experimental design to rapidly evolving developmental test articles and test facilities – often with great success. This paper discusses three case studies that span the range of USAF DT&E activities from EW to Ground Test to Flight Test and shows the truly revolutionary impact Fisher’s DOE can have on development. The Advanced Strategic and Tactical Expendable (ASTE) testing began in 1990 to develop, enhance, and test new IR flares, flare patterns, and dispense tactics. More than 60 aircraft & flare types have been tested. The typical output is a “Pancake Plot” of 200+ “cases” of flare, aspect angle, range, elevation, and flare effectiveness using a stop-light chart (red-yellow-green) approach. In usual testing – ~3000 flare engagements costing $1M to participate. The response, troublingly enough, is binary – 15-30 binomial response trials measuring P(Decoy). Binary responses are information-poor. Legacy testing does not assess present statistical power in reporting P(decoy) results. Analysts investigated replacing P(Decoy) w/ continuous metrics – e.g. time to decoy. This research is ongoing. We found we could spread the replicates out to examine 3x to 5x more test conditions without affecting power materially. Analysis with the Generalized Linear Model (GLZ) replaced legacy “cases” analysis with 75% improvement to confidence intervals with same data. We are seeking to build a Monte-Carlo simulation to estimate how many runs are required in a logistics regression model to achieve adequate power. We hope to reduce customer expenditures for flare information by as much as 50%. Co-authors J. Higdon, B, Knight. AEDC completed a major upgrade with new nozzle hardware to vary Mach. The Arnold Transonic Wind Tunnel 4T spans the range of flows from subsonic to approximately M9. The new wind tunnel was to be computer controlled. A number of key instrumentation improvements were made at the same time. The desire was to calibrate the resulting modified tunnel. The last calibration of 4T was 25 years ago in 1990. The calibration ranged across the full range of Mach and pressure capabilities, spanning a four-D space: pressure, Mach, wall angle, and wall porosity. Both the traditional OFAT effort – vary one factor at a time – and a parallel DOE effort were run to compare design, execution, modeling, and prediction capabilities against cost and time to run. The robust embedded face-centered CCD DOE design (J. Simpson and D. Landman ’05) employed 75 vs. 176 OFAT runs. The RSM design achieved 57% run savings. Due to an admirable discipline in randomization during the DOE trials, the smaller design required longer to run. As a result of using the DOE approach, engineers found it easier predict offcondition tunnel operating characteristics using RSM models, optimize facility flow quality for any given test condition. In addition, the RSM regression models support future “spot check” calibration in future by comparing predictions to measured values. If the measurement falls within the prediction interval, the existing calibration still appropriate. AEDC is using split-plot style designs a for current wind tunnel probe calibration. Co-author: Dr Dough Garrard.

Statistical engineering has been defined as: “The study of how to best utilize statistical concepts, methods, and tool, and integrate them with IT and other relevant sciences to generate improved results.” A key principle is that significant untapped benefits are often achievable by integrating multiple methods in novel ways to address a problem, without having to invent new statistical techniques. In this presentation, we discuss the application of statistical engineering to the problem of design and analysis of mixture experiments when process variables are also involved. In such cases, models incorporating interaction between the mixture and process variables have been developed, but tend to require large designs and models. By considering models nonlinear in the parameters, also well known in the literature, we demonstrate how experimenters can utilize an alternative, iterative strategy in attacking such problems. We show that this strategy potentially saves considerable experimental time and effort, while producing models that are nearly as accurate as much larger linear models. These results are illustrated using two published data sets and one new data set, all involving interactive mixture and process variable problems.

Co-authors: Dr. Darryl Ahner, Director, STAT COE Dr. Lenny Truett, STAT COE Mr. Scott Wacker, 96 TG/OL-ACS. This presentation will present the benefits of sequential testing and demonstrate how sequential testing can be used to address complex test conditions by developing well controlled early experiments to explore basic questions before proceeding to full-scale testing. This approach can result in increased knowledge and decreased cost. As of FY13 the Air Force had spent an estimated $47M on dry bay fire testing making fire the largest cost contributor for Live Fire Test and Evaluation (LFT&E) programs. There is currently an estimated 60% uncertainty in total platform vulnerable area (Av) driven by probability of kill (PK) due to ballistically ignited fires. A large part of this uncertain comes from the fact that current spurt modeling does not predict fuel spurt delay with reasonable accuracy despite a large amount of test data. A low-cost sequential approach was developed to improve spurts models. Initial testing used a spherical projectile to test 10 different factors in a definitive screening design. Once the list of factors was refined, a second phase of testing determined if a suitable methodology could be developed to scaled results using water as a surrogate for JP-8 fuel. Finally testing was performed with cubical projectiles to evaluate the effect of fragment orientation. The entire cost for this effort was less than one or two typical full-scale live fire tests.