Re-Computation of Numerical Results Contained in NACA Report No. 685

In an engineering note published in the Journal of Aircraft in the year 2000, Thomas A. Zeiler made generally known that some of the early works on aeroelastic flutter by Theodore Theodorsen and I.E. Garrick (NACA Report Nos. 496, 685, and 741) contained numerical errors in some of their numerical examples. Some of the plots containing numerical errors were later reproduced in two classic aeroelasticity texts (BAH and BA). Because these foundational papers and texts are often used in graduate courses on aeroelasticity, Zeiler recommended that an effort be undertaken to employ the computational resources available today (digital computers) to recompute the example problems in these early works and to publish the results to provide a complete and error-free set of numerical examples. This paper presents recomputed theoretical results contained in NACA Report No. 685 (NACA 685), Mechanism of Flutter, A Theoretical and Experimental Investigation of the Flutter Problem, by Theodore Theodorsen and I.E. Garrick. The recomputations were performed employing the solution method described in NACA 685, but using modern computational tools. With some exceptions, the magnitudes and trends of the original results were in good-to-excellent agreement with the recomputed results, a surprising but gratifying result considering that the NACA 685 results were computed by hand using pencil, paper, slide rules, and mechanical calculators called comptometers. Checks on the recomputations (about 25% were checked) were performed using the so-called -method of flutter solution. In all cases, including those where the original and recomputed results differed significantly, the checks were in excellent agreement with the recomputed results

Reinforcement Learning for Bandit Neural Machine Translation with Simulated Human Feedback

Machine translation is a natural candidate problem for reinforcement learning from human feedback: users provide quick, dirty ratings on candidate translations to guide a system to improve. Yet, current neural machine translation training focuses on expensive human-generated reference translations. We describe a reinforcement learning algorithm that improves neural machine translation systems from simulated human feedback. Our algorithm combines the advantage actor-critic algorithm (Mnih et al., 2016) with the attention-based neural encoder-decoder architecture (Luong et al., 2015). This algorithm (a) is well-designed for problems with a large action space and delayed rewards, (b) effectively optimizes traditional corpus-level machine translation metrics, and (c) is robust to skewed, high-variance, granular feedback modeled after actual human behaviors.Comment: 11 pages, 5 figures, In Proceedings of Empirical Methods in Natural Language Processing (EMNLP) 201

Computation of maximum gust loads in nonlinear aircraft using a new method based on the matched filter approach and numerical optimization

Time-correlated gust loads are time histories of two or more load quantities due to the same disturbance time history. Time correlation provides knowledge of the value (magnitude and sign) of one load when another is maximum. At least two analysis methods have been identified that are capable of computing maximized time-correlated gust loads for linear aircraft. Both methods solve for the unit-energy gust profile (gust velocity as a function of time) that produces the maximum load at a given location on a linear airplane. Time-correlated gust loads are obtained by re-applying this gust profile to the airplane and computing multiple simultaneous load responses. Such time histories are physically realizable and may be applied to aircraft structures. Within the past several years there has been much interest in obtaining a practical analysis method which is capable of solving the analogous problem for nonlinear aircraft. Such an analysis method has been the focus of an international committee of gust loads specialists formed by the U.S. Federal Aviation Administration and was the topic of a panel discussion at the Gust and Buffet Loads session at the 1989 SDM Conference in Mobile, Alabama. The kinds of nonlinearities common on modern transport aircraft are indicated. The Statical Discrete Gust method is capable of being, but so far has not been, applied to nonlinear aircraft. To make the method practical for nonlinear applications, a search procedure is essential. Another method is based on Matched Filter Theory and, in its current form, is applicable to linear systems only. The purpose here is to present the status of an attempt to extend the matched filter approach to nonlinear systems. The extension uses Matched Filter Theory as a starting point and then employs a constrained optimization algorithm to attack the nonlinear problem

Flutter suppression control law synthesis for the Active Flexible Wing model

The Active Flexible Wing Project is a collaborative effort between the NASA Langley Research Center and Rockwell International. The objectives are the validation of methodologies associated with mathematical modeling, flutter suppression control law development and digital implementation of the control system for application to flexible aircraft. A flutter suppression control law synthesis for this project is described. The state-space mathematical model used for the synthesis included ten flexible modes, four control surface modes and rational function approximation of the doublet-lattice unsteady aerodynamics. The design steps involved developing the full-order optimal control laws, reducing the order of the control law, and optimizing the reduced-order control law in both the continuous and the discrete domains to minimize stochastic response. System robustness was improved using singular value constraints. An 8th order robust control law was designed to increase the symmetric flutter dynamic pressure by 100 percent. Preliminary results are provided and experiences gained are discussed

Comparison of Theodorsen's Unsteady Aerodynamic Forces with Doublet Lattice Generalized Aerodynamic Forces

This paper identifies the unsteady aerodynamic forces and moments for a typical section contained in the NACA Report No. 496, "General Theory of Aerodynamic Instability and the Mechanism of Flutter," by Theodore Theodorsen. These quantities are named Theodorsen's aerodynamic forces (TAFs). The TAFs are compared to the generalized aerodynamic forces (GAFs) for a very high aspect ratio wing (AR = 20) at zero Mach number computed by the doublet lattice method. Agreement between TAFs and GAFs is very-good-to-excellent. The paper also reveals that simple proportionality relationships that are known to exist between the real parts of some GAFs and the imaginary parts of others also hold for the real and imaginary parts of the corresponding TAFs

MEMS Capacitive Strain Sensing Elements for Integrated Total Knee Arthroplasty Prosthesis Monitoring

Measuring the in vivo load state of Total Knee Arthroplasty (TKA) components is required to understand the structural environment and wear characteristics of the devices. The ability to acquire this information gives tremendous insight into the mechanics of the joint replacement prosthesis. Data corresponding to normal loads, in-plane loads, shear loads, load center, contact area, and the rate of loading is needed to fully understand the kinematics and kinetics of the orthopedic implant. In this research, a novel sensing system has been developed which is capable of fully characterizing three-dimensional strain and stress at a single location. Capacitance-based sensors were chosen to avoid the power loss and drift characteristics typical of resistive elements due to resistive heating effects. A design and optimization methodology has been developed by combining conformal mapping electrostatic analysis techniques with methods from micromechanics of composite materials. Results of the design and optimization technique are used to understand the behavior of the sensing system. Simulation of these systems was performed using multiphysics finite element analysis, and novel methods for fabricating the sensors were adapted from techniques for fabricating microelectromechanical systems (MEMS) using biocompatible materials. An array of six sensors was fabricated with a critical dimension of 2.25 micrometers. This array consisted of a parallel plate capacitor for measuring normal strain, two differential elements for sensing shear strain normal to the plane of the array, and three interdigitated transducer (IDT) elements for characterizing strain in the plane of the sensor. The normal strain sensor exhibited a sensitivity of 1.54×10-3 picofarads per megapascal, and the shear sensor had a sensitivity of 4.77×10-5 picofarads per megapascal. Testing results showed that all sensors had linear response to loading and insignificant drift. Multiaxial testing results illustrated the ability of the differential sensors to determine loading direction. A multiaxial, MEMS sensor array has been developed for use in orthopedic, load-measuring conditions. This system has been optimized for use in soft materials such as ultra-high molecular weight polyethylene (UHMWPE). In the future, arrays of sensors will be embedded in orthopedic components to determine the total state of stress at local positions within the component

A Study of the Retail and Wholesale Distribution of Frozen Foods in Tennessee

[From the Introduction] One of the most amazing stories to come from the foods business during the past decade is the growth of the frozen foods industry. Its rapid development, after having partially solved many perplexing problems of production and distribution, was somewhat accelerated by higher consumer incomes and wartime scarcities. Equally important is the fact that housewives have been relatively quick to adopt frozen foods. Therefore, today frozen foods are occupying an increasingly important position and the industry no longer considers itself as being in the infant stage of development

Identifying Cost Patterns of Managing Technology Transfer Actions

Significant national resources are dedicated to research and development (R&D) at government laboratories. In an era of increasing deficits and resulting budget reductions, transfer of technology from these laboratories to the private sector is important in order to improve the return on this R&D investment, as well as to improve the US industrial technological base, thus enhancing our nation\u27s economic security. However, no accurate measures to evaluate the efficiency of the technology transfer (TT) process exist. Likewise, accurate cost information, affording insight into the cost pattern and allowing more effective resource management, does not exist. This research draws on the principles of activity-based costing in order to develop a collection instrument, quantify the direct cost-over-time, and identify the cost patterns of eight TT projects managed at Wright Laboratory, all employing the cooperative research and development agreement vehicle. Results reveal 80 percent of a technology transfer\u27s total resources were dedicated to the performance of the transfer activity. Additionally, human resources accounted for 80 percent of the total. Expenditures were linear and fairly consistent over the project\u27s life, which begins nearly six months prior to signature and ends more than five months after expiration

An Investigation of the Overlap Between the Statistical Discrete Gust and the Power Spectral Density Analysis Methods

The results of a NASA investigation of a claimed Overlap between two gust response analysis methods: the Statistical Discrete Gust (SDG) Method and the Power Spectral Density (PSD) Method are presented. The claim is that the ratio of an SDG response to the corresponding PSD response is 10.4. Analytical results presented for several different airplanes at several different flight conditions indicate that such an Overlap does appear to exist. However, the claim was not met precisely: a scatter of up to about 10 percent about the 10.4 factor can be expected