Active subspace methods in theory and practice: Or, does your model really have lots of parameters?
11 Apr 2014 | Online Presentations | Contributor(s): Paul G. Constantine
Science and engineering models typically contain multiple parameters representing input data---e.g., boundary conditions or material properties. The map from model inputs to model outputs can be viewed as a multivariate function. One may naturally be interested in how the function changes as...
MD Simulations of Gas Flows in Nano-Channels and Interface Thermal Resistance Between Simple Liquids and Solids
31 May 2012 | Online Presentations | Contributor(s): Ali Beskok
This talk focuses on our group’s recent research on molecular dynamics simulations of gas flows in nano-scale confined geometries, and interface thermal resistance between simple liquids and solids. Gas flow research demonstrates the importance of wall force field effects that penetrate...
Multiscale Considerations in DNS Studies of Multiphase Flows
31 May 2012 | Online Presentations | Contributor(s): Gretar Tryggvason
Here we discuss such simulations from a multi-scale perspective, focusing on two aspects: First of all, DNS results can help with the development of closure relations of unresolved processes in simulations of large-scale “industrial” systems. As an example we discuss recent results for...
Application-driven Co-Design: Using Proxy Apps in the ASCR Materials Co-Design Center
31 May 2012 | Online Presentations | Contributor(s): Jim Belak
Computational materials science is performed with a suite of applications that span the quantum mechanics of interatomic bonding to the continuum mechanics of engineering problems and phenomenon specific models in between. In this talk, we will review this suite and the motifs used in each of...
Exascale Co-design for Materials in Extreme Environments: Heterogeneous Algorithms for Heterogeneous Architectures
30 May 2012 | Online Presentations | Contributor(s): Timothy C. Germann
Computational materials scientists have been among the earliest and heaviest users of leadership-class supercomputers. The codes and algorithms which have been developed span a wide range of physical scales and have been useful not only for gaining scientific insight, but also as testbeds for...
Micromechanics of Polycrystals: Full-field Computations and Second-order Homogenization Approaches
30 May 2012 | Online Presentations | Contributor(s): Ricardo Lebensohn
In the first part of this talk we will present a spectral formulation based on crystal plasticity and Fast Fourier Transforms (FFT) for the determination of micromechanical fields in plastically-deformed 3-D polycrystals. This formulation, pioneered by Suquet and coworkers as a fast algorithm to...
Near-field radiative heat transfer and Casimir Force Measurement
30 May 2012 | Online Presentations | Contributor(s): Joel Chevrier
This presentation first makes a simple introduction on how the charge fluctuations give rises to these effects that are nowadays most effectively detected using MEMS or AFM technologies. This will lead to question the relevance of these effects in the use of MEMS. After description of our...
Particle Simulations of Ion Generation and Transport in Microelectromechanical Systems and Micropropulsion
29 May 2012 | Online Presentations | Contributor(s): Venkattraman Ayyaswamy
The first part of the talk deals with use of the PIC method with Monte Carlo collisions (MCC) between electrons and the ambient neutral gas to develop models to predict charge accumulation, breakdown voltage, etc. for various ambient gases, gap sizes, cathode material, and frequency of applied...
Quantifying Uncertainties from the Grid in CFD Solutions
03 Jan 2012 | Online Presentations | Contributor(s): Tom I-P. Shih
This talk begins with a study on grid-quality measures that assume grid-induced errors in a CFD solution at a cell is a function of the cell size and shape, the grid distribution around that cell, and the solution computed in the neighborhood of that cell.
Verification and Validation in Simulations of Complex Engineered Systems
03 Jan 2012 | Online Presentations | Contributor(s): Robert Moser
Computational simulation is a ubiquitous tool in engineering. Further, the explosion of computational capabilities over the last several decades has resulted in the use of computational models of unprecedented complexity to make critical design and operation decisions. One potential benefit...
Experiments and Models Regarding Strain Dependent Thermal Conductivity and Strength at the Nanoscale and Microscale
22 Sep 2011 | Online Presentations | Contributor(s): Vikas Tomar
Silicon micro- and nano-structures are essential in today’s integrated circuits and sensors. The functioning and performance of such devices are highly affected by thermal properties. Due to the size effect, the thermal properties of bulk silicon cannot represent those of silicon...
Mesoscopic Simulations of Nitromethane
22 Sep 2011 | Online Presentations | Contributor(s): Jean-Bernard Maillet
We present recent developments on the dissipative particle model that allow simulating the physico-chemical behavior of a molecular material at the mesoscale level. Several ingredients have been added to the previous model, in particular concerning the intermolecular force field and the...
Development of the ReaxFF reactive force fields and applications to combustion, catalysis and material failure
12 Sep 2011 | Online Presentations | Contributor(s): Adri van Duin
This lecture will describe how the traditional, non-reactive FF-concept can be extended for application including reactive events by introducing bond order/bond distance concepts. Furthermore, it will address how these reactive force fields can be trained against QM-data, thus greatly enhancing...
Emerging Opportunities, Challenges, and Applications in Exascale Computing
10 Mar 2011 | Online Presentations | Contributor(s): Ananth Grama
The move towards exascale computing platforms (capable of 10^18 floating point operations) poses tremendous challenges, while presenting opportunities for foundational advances in a variety of application domains. In this talk, I will describe various technical issues that must be overcome to...
Peanuts vs. Pyramids: Two Perspectives on MEMS
29 Dec 2009 | Online Presentations | Contributor(s): Stephen D. Senturia
MEMS, the acronym for Micro-electromechanical Systems, also known simply as “Micro-systems,” come in two main types: commodity products (the peanuts) and MEMS-enabled products (the pyramids, or, more correctly, the inverted pyramids). The economics of scale greatly affect how these two...
Molecular Sensors for MEMS
10 Dec 2009 | Online Presentations | Contributor(s): John P. Sullivan
This seminar will cover the issues involved in using molecular sensors in MEMS and their application to microchannels, supersonic micronozzles, microjet impingement, microturbines and unsteady fluidic actuators.
Nanotribology, Nanomechanics and Materials Characterization Studies
08 Jun 2009 | Online Presentations | Contributor(s): Bharat Bhushan
Fundamental nanotribological studies provide insight to molecular origins of interfacial phenomena including adhesion, friction, wear and lubrication. Friction and wear of lightly loaded micro/nano components are highly dependent on the surface interactions (few atomic layers). Nanotribological...
The Challenges of Micro-System Product Development
05 Jun 2009 | Online Presentations | Contributor(s): James J. Allen
This talk will discuss the historical development of micro‐system technology, the products that have been developed and the challenges to development of a reliable product.
Experiences with nonintrusive polynomial Chaos and stochastic collocation methods for uncertainty analysis and design
13 Mar 2009 | Online Presentations | Contributor(s): Michael S. Eldred
Non—intrusive polynomial chaos expansion (PCE) and stochastic collocation (SC) methods are attractive techniques for uncertainty quantification due to their abilities to produce functional representations of stochastic variability and to achieve exponential convergence rates in statistics of...
Gas Damping of Microcantilevers at Low Ambient Pressures
03 Nov 2008 | Online Presentations | Contributor(s): Rahul Anil Bidkar
This seminar will present a theoretical model for predicting the gas damping of long, rectangular silicon microcantilevers, which are oscillating in an unbounded gaseous medium with the ambient pressures varying over 5 orders of magnitude (1000 > Kn > 0.03). The work is the result of a...
From density functional theory to defect level in silicon: Does the “band gap problem” matter?
01 Oct 2008 | Online Presentations | Contributor(s): Peter A. Schultz
Modeling the electrical effects of radiation damage in semiconductor devices requires a detailed description of the properties of point defects generated during and subsequent to irradiation. Such modeling requires physical parameters, such as defect electronic levels, to describe carrier...