Conferences, Lectures, & Seminars
Events for April
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Modeling the Flow Response of Severely Processed Metals: Application to Copper and Zirconium
Wed, Apr 11, 2007 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Irene J. Beyerlein Staff Scientist Theoretical Division Los Alamos National Laboratory Los Alamos, NM 87545 Irene@lanl.gov Severe plastic deformation techniques have received considerable attention for their potential in producing nanocrystalline metals with outstanding properties. As the name suggests, these techniques involve deforming metals up to extremely large strains, from 100% to 1600%. To measure their mechanical performance, subsequent uniaxial tests or hardness measurements are conducted on the heavily processed samples. In most situations, the severely processed material is plastically anisotropic, meaning that the yield stress and hardening evolution depend on the strain mode and direction imposed by the test. So for example the tensile strength of the material could be stronger along the billet axis than transverse to it. The opposite may occur in compression. Furthermore, subsequent loading most often imposes a strain-path change to the material. Both strain-path changes and large plastic straining have for some time challenged development of models for metal deformation. We are currently developing micromechanical hardening laws and multi-scale models for the deformation behavior of metals with a large strain processing history. The resulting constitutive model accounts for contributions to anisotropy by texture and microstructural evolution in pre-straining and re-loading. In this talk, the predictions will be compared with the measured responses in copper and zirconium after they have been processed by equal channel angular extrusion. The model forecasts significant asymmetry in the tension and compression responses and directional dependence of these metals after ECAE, in agreement with observation
Location: Seaver Science LIbrary (SSL) Rm 150
Audiences: Everyone Is Invited
Contact: April Mundy
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Laufer Keynote Lecture
Wed, Apr 18, 2007 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Reflections on the Turbulence Problem Anatol Roshko Theodore von Kármán Professor of Aeronautics Graduate Aeronautical Laboratories California Institute of TechnologyPasadena, CAReception: 2:30PM-3:30 PMSeminar 3:30PM-4:30PM The turbulence problem has been around a long timesince the latter part of the 19th century. Toward the end of his large book on Hydrodynamics, Edition 3, 1906, Lamb opens the section on "Turbulent Motion" with the statement, "It remains to call attention to the chief outstanding difficulty of our subject." Since then the importance has not diminished and the "difficulty" continues to get unprecedented attention. Because of its importance as an "unsolved problem" of physics and an ongoing problem for engineering, ideas about its solution and support for its clarification continue to develop. But just what is the "turbulence problem", or problems, and what might be the "solution", or solutions? This talk explores those questions in the historical background of the various developments, ideas and characters that have participated.
Location: Ethel Percy Andrus Gerontology Center (GER) - ontology Auditorium
Audiences: Everyone Is Invited
Contact: April Mundy
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Distributed and Networked Systems: An Overview, and New Directions
Mon, Apr 23, 2007 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Demetri Spanos Post-Doctoral ScholarCalifornia Institute of Technology Pasadena, CA This talk will address some of the main themes in distributed and networked systems engineering, as well as some specific research results focused on a modeling and design framework for certain distributed systems. We will begin with a (very) short history, and discuss why this field has experienced a revival in academia, industry, and government spending over the last decade. We will also present some less traditional views on future applications of distributed systems engineering, especially in the design of aerospace, mechanical, structural, and other "physically embedded" systems. The latter part of the presentation will address a collection of recent research results, a modeling and design framework based on the concept of a "distributed gradient". As an application, we will discuss a widely studied architecture for control based on spatially averaged quantities, and show this to be a special case of the distributed gradient framework. If time permits, we will also discuss a wide variety of novel systems following from the principles of a distributed gradient system
Location: Seaver Science Library )SSL) Rm 150
Audiences: Everyone Is Invited
Contact: April Mundy
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Constrained Variation in Multiscale Simulations of Micro- and Nano-Fluidics and Subgrid-Scale Stress
Wed, Apr 25, 2007 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Shiyi Chen Alonzo G. Decker Jr. Chair in Engineering and Science Department of Mechanical Engineering The Johns Hopkins University Baltimore, MD Finding physically consistent solutions in multiscale methods is crucial for various multiscale modeling and simulations. A framework for continuum and molecular dynamics hybrid multiscale method has been recently developed to simulate micro- and nano-fluid flows. In this approach, the continuum Navier-Stokes equation is used in one flow region and atomistic molecular dynamics in another. The spatial coupling between two methods is achieved through the constrained dynamics in an overlap region. The proposed multiscale method has been validated in simple fluid flows, including sudden-start Couette flow and channel flow with nano-scale wall roughness, showing quantitative agreement with results from analytical solutions and full molecular dynamics simulations. The hybrid method is then used to study the singularity problems in the driven cavity and moving contact lines. Following the stress over more than six decades in length in systems with characteristic scales of millimeters and milliseconds allows us to resolve the singularity and determine the force for the first time. The speedup over pure atomistic calculation is more than fourteen orders of magnitudes. The similar idea of constrained variation has also been used for developing constrained dynamic subgrid-scale (C-SGS) stress model of fluid turbulence. In the C-SGS, we impose physical constraints in the dynamic procedure of calculating the SGS coefficients. In particular, we study dynamic mixed models with energy flux and helicity flux constraints. The comparison between the large eddy simulation results in steady and decaying isotropic turbulence using constrained and non-constrained SGS models and those from direct numerical simulation (DNS) will be presented. It is found that the C-SGS not only predicts the turbulent dissipation more accurately, but also shows a strong correlation between the model stress and the real stress from a priori test, which is a desirable feature combining the advantages of dynamic Smagorinsky and traditional mixed models.
Location: Seaver Science Llibrary (SSL) Room 150
Audiences: Everyone Is Invited
Contact: April Mundy