A digital computer program for studying elasto-plastic structural behavior due to cyclic loading

A computer program has been developed to study the behavior of plane stress structures under cyclic loading. Such phenomena as thermal ratcheting, alternate plasticity, shake-down and the Bauschinger effect may be considered. The incremental theory of plasticity has been used. The program deals with realistic conditions such as nonlinear strain hardening, nonlinear temperature distribution and occurrence of both compressive and tensile plastic flow. The concept of an average material property has been used. Thermal ratcheting of a beam subjected to a constant bending moment and a temperature cycle has been studied in detail. The analysis shows analytically that the rate of plastic strain growth reduces with an increase in the number of loading cycles. Applications of the computer program have been discussed. Further, the thermal ratcheting of a two bar model has been discussed considering the simplifying assumptions of linear strain hardening and the absence of compressive plastic flow --Abstract, page ii

Code validation for the simulation of supersonic viscous flow about the F-16XL

The viewgraphs and discussion on code validation for the simulation of supersonic viscous flow about the F-16XL are provided. Because of the large potential gains related to laminar flow on the swept wings of supersonic aircraft, interest in the applications of laminar flow control (LFC) techniques in the supersonic regime has increased. A supersonic laminar flow control (SLFC) technology program is currently underway within NASA. The objective of this program is to develop the data base and design methods that are critical to the development of laminar flow control technology for application to supersonic transport aircraft design. Towards this end, the program integrates computational investigations underway at NASA Ames-Moffett and NASA Langley with flight-test investigations being conducted on the F-16XL at the NASA Ames-Dryden Research Facility in cooperation with Rockwell International. The computational goal at NASA Ames-Moffett is to integrate a thin-layer Reynolds averaged Navier-Stokes flow solver with a stability analysis code. The flow solver would provide boundary layer profiles to the stability analysis code which in turn would predict transition on the F-16XL wing. To utilize the stability analysis codes, reliable boundary layer data is necessary at off-design cases. Previously, much of the prediction of boundary layer transition has been accomplished through the coupling of boundary layer codes with stability theory. However, boundary layer codes may have difficulties at high Reynolds numbers, of the order of 100 million, and with the current complex geometry in question. Therefore, a reliable code which solves the thin-layer Reynolds averaged Navier-Stokes equations is needed. Two objectives are discussed, the first in greater depth. The first objective is method verification, via comparisons of computations with experiment, of the reliability and robustness of the code. To successfully implement LFC techniques to the F-16XL wing, the flow about the leading edge must be maintained as laminar flow. Therefore, the second objective is to focus on a series of numerical simulations with different values of angle of attack, alpha, and Reynolds numbers. The purpose of the simulations is to study their effects on the two main factors which precipitate transition to turbulence at leading edges of highly swept wings (e.g., 'spanwise contamination' and 'crossflow instability')

A method for three-dimensional flow analysis in a rotor using a high speed digital computer

Theoretical analyses of flow with rotating passages of turbi0machinery have become necessary for the proper design of turbo-pump elements in liquid fuel boosters and power conversion units. One such theory is presented, and a numerical solution derived. this theory develops a method for the analysis of steady, inviscid, adiabatic flow through arbitrary rotors. A detailed analysis in a meridional plane is given, assuming axial symmetry. A simplified approach to the blade to blade solution is also presented. The merits of these theories are compared with other proposed methods. The inverse, or design, approach is considered, and found to be unnecessary. A numerical solution for incompressible flow is derived and applied to the flow solution in the impeller of a mixed flow compressor with backwards-bent blades of arbitrary shape. Meridional streamlines and relative vorticity distributioins are progressively calculated on a CDC 1604 computer, using FORTRAN program language. Data are measured from a detailed presentation of the blade shape in a meridional plane. Blade to blade relative velocity distributions are calculated from the meridional plane analysis. It is concluded that the results completely define the flow and are sufficiently accurate for engineering applications. Validation is based upon the reliability of the theory, and upon comparisons with results of other methods. Extensions of the scope of this approach are recommended, which include the compressible solution and the solution of flows in unbladed passages.http://www.archive.org/details/methodforthreedi00feltLieutenant Commander, United States NavyApproved for public release; distribution is unlimited

Approximate Computation and Implicit Regularization for Very Large-scale Data Analysis

Database theory and database practice are typically the domain of computer scientists who adopt what may be termed an algorithmic perspective on their data. This perspective is very different than the more statistical perspective adopted by statisticians, scientific computers, machine learners, and other who work on what may be broadly termed statistical data analysis. In this article, I will address fundamental aspects of this algorithmic-statistical disconnect, with an eye to bridging the gap between these two very different approaches. A concept that lies at the heart of this disconnect is that of statistical regularization, a notion that has to do with how robust is the output of an algorithm to the noise properties of the input data. Although it is nearly completely absent from computer science, which historically has taken the input data as given and modeled algorithms discretely, regularization in one form or another is central to nearly every application domain that applies algorithms to noisy data. By using several case studies, I will illustrate, both theoretically and empirically, the nonobvious fact that approximate computation, in and of itself, can implicitly lead to statistical regularization. This and other recent work suggests that, by exploiting in a more principled way the statistical properties implicit in worst-case algorithms, one can in many cases satisfy the bicriteria of having algorithms that are scalable to very large-scale databases and that also have good inferential or predictive properties.Comment: To appear in the Proceedings of the 2012 ACM Symposium on Principles of Database Systems (PODS 2012

Conic Optimization Theory: Convexification Techniques and Numerical Algorithms

Optimization is at the core of control theory and appears in several areas of this field, such as optimal control, distributed control, system identification, robust control, state estimation, model predictive control and dynamic programming. The recent advances in various topics of modern optimization have also been revamping the area of machine learning. Motivated by the crucial role of optimization theory in the design, analysis, control and operation of real-world systems, this tutorial paper offers a detailed overview of some major advances in this area, namely conic optimization and its emerging applications. First, we discuss the importance of conic optimization in different areas. Then, we explain seminal results on the design of hierarchies of convex relaxations for a wide range of nonconvex problems. Finally, we study different numerical algorithms for large-scale conic optimization problems.Comment: 18 page

Combining behavioural types with security analysis

Today's software systems are highly distributed and interconnected, and they increasingly rely on communication to achieve their goals; due to their societal importance, security and trustworthiness are crucial aspects for the correctness of these systems. Behavioural types, which extend data types by describing also the structured behaviour of programs, are a widely studied approach to the enforcement of correctness properties in communicating systems. This paper offers a unified overview of proposals based on behavioural types which are aimed at the analysis of security properties