Seminars

Thursday, April 17, 2014 - 11:45am | Schiciano Auditorium Side B
David Ewins, FRS

 

In most aerospace structures there are two primary concerns: performance  - often dictated by thermo-fluid considerations, and integrity - which is heavily influenced by materials and structural dynamics.  This talk is concerned with the latter aspect, and the efforts which are under way to improve this aspect of the state-of-the-art aerospace designs of the future. The first part of the talk is essentially a strategic overview of the whole area of Structural Dynamics, seeking to identify some of the crucial topics that present the most urgent challenges for further progress.  At the strategic level, the first issue is the critical importance of obtaining the correct balance between the three core competences that must be deployed in almost every application – Theoretical Modelling, Numerical Analysis and Experimental Measurement.  Then, the focus turns to ensure that the integration of  test analysis activities which is necessary to carry out Validation and Verification of models, designs and products  are properly and effectively carried out, including  full attention to all sources of uncertainty.

 

The second part of the talk describes some of the recent specific developments in the aero-engine and rotorcraft sectors.  First amongst these is the importance, and challenges, of taking proper account of the interfaces and joints which separate the many components in any engineering structure.  This leads inevitably to much more frequent encounters with nonlinear behaviour, and the need for both modelling and - especially - experimental methods to deal with these effects.  Of particular interest throughout is the need to provide technology capabilities that allow industry to be able to analyse, design and test for realistic in-service operating conditions. 

Past Seminars

Friday, April 11, 2014 - 11:30am | Schiciano Auditorium Side B
Prof. Alexander J. Smits

 

Logarithmic scaling is one of the corner stones of our understanding of wall-bounded turbulent flows. In 1938, Clark B. Millikan advanced an overlap argument that framed the logarithmic variation of the mean velocity in simple dimensional terms.  Seventy-five years later, however, basic aspects of this logarithmic region, such as its slope (described by von Karman’s constant), and its spatial extent, are still being debated. In addition, Townsend in 1976 proposed a logarithmic scaling for the streamwise and spanwise components of turbulence based on the attached eddy hypothesis, but to date the experimental verification has been elusive. Here, we use pipe flow measurements over a very large Reynolds number range to examine these expectations of logarithmic scaling, and show that pipe flows at sufficiently high Reynolds number reveal both expected and unexpected implications for our understanding and our capacity to model turbulence.

Dr. Smits is the Eugene Higgins Professor of Mechanical and Aerospace Engineering at Princeton, as well as a Professorial Fellow at Monash University in Australia.  His research interests are centered on fundamental, experimental research in turbulence and fluid mechanics. In 2004, Dr. Smits received the Fluid Dynamics Award of the AIAA.  In 2007, Dr. Smits received the Fluids Engineering Award from the American Society of Mechanical Engineers (ASME), the Pendray Aerospace Literature Award from the American Institute of Aeronautics and Astronautics (AIAA), and the President's Award for Distinguished Teaching from Princeton University. He is a Fellow of the American Physical Society, the American Institute of Aeronautics and Astronautics, the American Society of Mechanical Engineers, the American Academy for the Advancement of Science, the Australasian Fluid Mechanics Society, and he is a Member of the National Academy of Engineering.

Monday, March 17, 2014 - 11:45am | 115 Teer
John Kitchin, Carnegie Mellon University

Electrochemical water oxidation may play a crucial role in future renewable energy systems for energy storage, fuel synthesis, and integration with oxycombustion systems. Some outstanding challenges in efficiently oxidizing water remain, including the overly high energetic cost of water electrolysis, and the high cost of materials that perform moderately well. Many efforts have focused on searching for new oxide-based materials with enhanced performance, but no exceptional material has been found to date that is substantially better than known materials. We will show a simple model based on thermodynamics and parameterized by density functional theory that suggests there is an upper bound in activity oxide-based materials that may explain why substantially better materials have not yet been found, and that suggests what must be done to find better materials. We will highlight some challenges in the accuracy of the model, both on the experimental side of what is actually modeled, and on the computational side of the methods used for the modeling. We will illustrate a new, more accurate computational methodology and our plans to use that in pushing the next evolution in water oxidation forward.

Biography: John Kitchin completed his B.S. in Chemistry at North Carolina State University. He completed a M.S. in Materials Science and a PhD in Chemical Engineering at the University of Delaware in 2004 under the advisement of Dr. Jingguang Chen and Dr. Mark Barteau. He received an Alexander von Humboldt postdoctoral fellowship and lived in Berlin, Germany for 1 ½ years studying alloy segregation with Karsten Reuter and Matthias Scheffler in the Theory Department at the Fritz Haber Institut. Professor Kitchin began a tenure-track faculty position in the Chemical Engineering Department at Carnegie Mellon University in January of 2006. He is currently an Associate Professor. At CMU, Professor Kitchin is active in a major research effort within the National Energy Technology Laboratory Regional University Alliance in CO2 capture, chemical looping and superalloy oxidation. Professor Kitchin also uses computational methods to study adsorbate-adsorbate interactions on transition metal surfaces for applications in catalysis. He was awarded a DOE Early Career award in 2010 to investigate multifunctional oxide electrocatalysts for the oxygen evolution reaction in water splitting using experimental and computational methods. He received a Presidential Early Career Award for Scientists and Engineers in 2011.

This seminar is co-sponsored by the Duke Energy Initiative as part of the Energy Research Seminar Series.

 

Wednesday, February 5, 2014 - 12:00pm | Hudson 208
Gus Hart, Brigham Young University

The talk will first address the state of the art in materials prediction, the "grand challenges," and propose one direction forward. The second part will discuss "compressive sensing" as an approach to make that direction viable.

Thursday, January 9, 2014 - 12:00pm | Hudson 232
Noa Marom, Tulane University

The development of solar cells is driven by the need for clean and sustainable energy. Organic and dye sensitized cells (DSC) are considered as promising alternatives for traditional single crystal silicon cells, particularly for large area, low cost applications. However, the efficiency of such cells is still far from the theoretical limit.

First-principles quantum mechanical simulations may be used for computer-aided design of new materials, material combinations, and nano-structures for more efficient organic and dye-sensitized cells. To this end, it is important to obtain an accurate description of the electronic structure, including the fundamental gaps and energy level alignment at interfaces. This requires a treatment beyond ground-state density functional theory (DFT). Within the framework of many-body perturbation theory (MBPT), these properties may be calculated using the GW approximation, where G is the one-particle Green's function and W is the dynamically screened Coulomb potential.

In this talk I will provide an introduction to GW methods and demonstrate their applications to the components of organic and dye-sensitized solar cells: TiO2 clusters , organic semiconductors, dyes, and dye-sensitized TiO2 clusters.

Biography: Noa Marom has an interdisciplinary background in physics, materials science, and chemistry (she holds degrees in all three). She received her Ph.D. in 2010 from the Weizmann Institute of Science in her home country of Israel and was awarded the Shimon Reich Memorial Prize of Excellence for her. She pursued postdoctoral research at the Institute for Computational Engineering and Sciences (ICES) at the University of Texas at Austin. She has recently joined the Physics and Engineering Physics Department at Tulane University in New Orleans. Her field of research is computational materials science. She is particularly interested in the electronic properties of the organic-inorganic interfaces, found in organic and dye-sensitized solar cells, and in van der Waals interactions in molecular crystals and other weakly bound systems. She is working toward computational design of materials, interfaces, and nanostructures.

(This seminar is co-sponsored by the Duke Energy Initiative.)

Monday, November 18, 2013 - 12:00pm | HUDSON 222
Linyou Cao, NCSU

Two-dimensional (2D) transition metal chalcogenide (TMDC) materials with a monolayer or few-layer of atoms have been emerging as the cutting edge of physical science and engineering.  These materials may open up new opportunities for a variety of fields, including surface science, catalysis, semiconductor technology, energy conversion, and flexible devices.

In this talk, I will first introduce the controlled scalable synthesis that we have recently developed for the growth of centimeter-scale, high quality, and uniform monolayer and fewlayer MoS2 films.  These films with atomically defined physical features provide an unprecedented platform for us to study the fundamentals in catalysis and photonics. To illustrate this notion, I will show our recent results in the layer-dependent catalytic activities and exciton dynamics of MoS2 films.

Biography: Dr. Linyou Cao is an assistant professor of Materials Science and Engineering at North Carolina State University.  He received his PhD degree in the Department of Materials Science and Engineering at Stanford in 2010, and held a Miller Research Fellowship at the University of California, Berkeley prior to joining the faculty of NCSU August  2011.  His group works on the catalysis and photonics of two-dimensional (2D) materials as well as dielectric metamaterials. Dr. Cao received a Ralph E. Powe Junior Faculty Enhancement Award from the Oak Ridge Associated Universities in 2012 and a Young Investigator Award from the Army Research Office in 2013.

 

 

Wednesday, November 6, 2013 - 12:00pm | HUDSON 212
Yong Zhu, NCSU

Recent advance in nanotechnology has brought about a host of nanomaterials, such as nanoparticles, nanowires, nanotubes and graphene that exhibit ultrahigh strength (e.g., sample-wide stress > 1/10 of their ideal strengths). Such nanomaterials are not only an ideal platform to study fundamental mechanics, but also important building blocks for a broad spectrum of nanotechnology applications. Here I present three related examples. The first example is on in-situ scanning and transmission electron microscopy (SEM/TEM) mechanical testing of crystalline nanowires. I will highlight metallic nanowires with Ag as an example. Ag nanowires exhibit strong size dependent elastic modulus and yield strength. Its unique five-fold twinned structure gives rise to the strain hardening behavior. The second example is on the interface mechanics between graphene and polymer substrates. Two interfacial failure mechanisms, shear sliding under tension and buckling under compression, are identified for monolayer graphene on plastic substrate using in-situ Raman and atomic force microscopy measurements. A nonlinear shear-lag model is used to relate the measurements to the interfacial properties including the shear strength and efficiency for stress transfer. I will conclude my talk with the third example, which is stretchable electronics based on 1D nanomaterials. I will discuss a particular type of device, highly conductive and stretchable electrodes based on Ag nanowires.

Biography:  Yong Zhu received his B.S. degree in Mechanics and Mechanical Engineering from the University of Science and Technology of China, China (1999), and his M.S. (2001) and Ph.D. (2005) degrees in Mechanical Engineering from Northwestern University. After a postdoctoral fellow at the University of Texas at Austin, he joined the Department of Mechanical and Aerospace Engineering at North Carolina State University in 2007, where he is currently an Associate Professor.  Dr. Zhu’s research interests lie at the interface between solid mechanics and micro/nano-technology, including mechanical properties and multiphysical coupling of nanostructures, micro/nano-electromechanical systems, flexible/stretchable devices for healthcare applications, and adhesion/friction of nanostructures. He has received several awards including Best Poster Award in the Gordon Research Conference on Thin Film & Small Scale Mechanical Behavior (2006), Sigma Xi Faculty Research Award (2012) and Society of Experimental Mechanics Young Investigator Award (2013).

Wednesday, October 30, 2013 - 12:00pm | Hudson 212
Sergey Levchenko

Doping, either intentional or unintentional, can affect charge state, concentration, and distribution of defects in a material. Although different aspects of this influence had been discussed in literature, their relative significance and completeness are still debatable. Experiments measuring defect concentrations as a function of thermodynamic variables (T, p, doping) are scarce. On the other hand, previous theoretical approaches have aimed at a description of isolated defects, or, more recently, dopant-defect complexes. In this work, we demonstrate that these approaches missed an important part of the free energy that can greatly influence defect concentrations. Dopants introduce charge carriers, either holes (p-type) or electrons (n-type). The charge carriers can occupy defect electronic levels, leading to charging of both the dopants and the defects. Due to the long-range nature of the Coulomb interaction, the electrostatic energy of this charge separation strongly depends on the concentration and distribution of defects and dopants. Thus, in addition to the local contributions to the free energy of defect formation, such as breaking or making bonds and local lattice distortions, there is a global contribution due to the overall electrostatic energy of the system. We show that this global contribution can be significant at realistic conditions.

Biography: Sergey V. Levchenko is currently leading the research group "Unifying concepts in catalysis" at the Fritz Haber Institute of the Max Planck Society in Berlin, Germany. He received his M.Sc. degree in applied physics and mathematics from the Moscow Institute of Physics and Technology, Moscow, Russia, in 1997, and his Ph.D. in physical chemistry from the University of Southern California, Los Angeles, CA, in 2005. From 2005 to 2008, he was a post-doctoral researcher at the University of Pennsylvania, Philadelphia, PA, conducting research in the areas of complex ferroelectric oxides, surface science, and catalysis. His current research is focused on first-principles modelling of materials for heterogeneous catalysis, in particular defects at oxide surfaces, at realistic temperature and pressure conditions.

Wednesday, October 23, 2013 - 12:00pm | Hudson 212
Wei Hong, Iowa State Univeristy

Consisting of a crosslinked network of both hydrophobic and hydrophilic groups, a temperature-sensitive gel may collapse by expelling a large amount of solvent when heated over the lower critical solution temperature. For smaller samples which undergo a slow temperature change, this phase transition is homogeneous and the resultant deformation is uniform. When superheated, a relatively large gel may develop heterogeneous structures by nucleating solvent-rich domains inside. A Ginzburg-Landau-type phase-field model is formulated to study the microstructure evolution in a phase-separating gel. Numerical calculations show that the phase-separated domains coarsen non-self-similarly and form a spongy structure with thin walls of the dryer phase. Theoretical model further confirms that such a structure the deformation in each phase is more uniform, as favored by the energy of mixing. Furthermore, it is found that the coarsening will give way to a domain dilation mechanism if the system is brought to a far-from-equilibrium state. The thermodynamic and kinetic processes revealed by the models may help in designing stimuli-responsive soft machines, and in understanding similar phenomena in natural and biological systems.

Biography: Trained as a solid mechanician, Wei Hong’s expertise is in the theoretical modeling on the physics of materials and structures and his current research interest is in the behaviors of smart and soft materials under multiphysics fields, such as the instability and fracture of soft solids, phase-transition-induced toughening, and dielectric breakdown.  Dr. Hong got his B.S. (2000) and M.S. degrees (2002) both from Tsinghua University (Beijing, China).  Following his Ph.D. in Engineering Sciences (2006) at Harvard University, he was a postdoctoral fellow in the School of Engineering and Applied Sciences at Harvard, before joining the faculty of Iowa State.  Since 2008, Dr. Hong has been an assistant professor in the Department of Aerospace Engineering at Iowa State University, where he also holds courtesy appointments from the departments of Materials Science and Engineering and Mechanical Engineering.

Wednesday, October 2, 2013 - 12:00pm | Hudson 212
Andrew Alleyne, UIUC

High precision motion control is essential for a wide variety of modern applications.  The key to high precision is the incorporation of feedforward information along with typical feedback algorithms.  Iterative Learning Control is a very popular method to determine signal-based feedforward control.  This talk will discuss recent developments in improving the performance of ILC schemes and their applications to manufacturing applications.  In particular, we will motivate the use of ILC schemes with precision manufacturing applications particular to the nanoscale.  We begin by detailing components of a heterogeneous integration approach to manufacturing of novel electronic and photonic devices by fluidic and ionic transport.  This is part of an interdisciplinary research effort involving Materials Science, Physics, Chemistry, Manufacturing, and Controls.  The particular process to be detailed is a printing process, termed electro-hydrodynamic Jet (or e-Jet) printing, that is currently superior to most other printing approaches in terms of resolution.

After the demonstration of manufacturing processes, a brief introduction to Iterative Learning Control (ILC) will be given.  ILC is a novel adaptive technique that allows us to learn repeated trajectories and maximize precision in the automation machinery used for fabrication.  After an overview, the rest of the talk will discuss recent developments in ILC for both single axis and multi-axis systems.  We demonstrate the benefits in performance with numerical and experimental results.

Biography: Professor Alleyne received his B.S. in Engineering Degree from Princeton University in 1989 in Mechanical and Aerospace Engineering.  He received his M.S. and Ph.D. degrees in Mechanical Engineering in 1992 and 1994, respectively, from The University of California at Berkeley.  He joined the Department of Mechanical and Industrial Engineering at the University of Illinois, Urbana-Champaign in 1994 and is also appointed in the Coordinated Science Laboratory of UIUC.  He currently holds the Ralph M. and Catherine V. Fisher Professorship in the College of Engineering. He was awarded the ASME Dynamics Systems and Control Division’s Outstanding Young Investigator Award and was a Fulbright Fellow to the Netherlands where he held a Visiting Professorship in Vehicle Mechatronics at TU Delft.  He is the recipient of the 2008 ASME Gustus L. Larson Memorial Award and is also a Fellow of ASME.  His research interests are a mix of theory and implementation with a broad application focus. In addition to research he has a keen interest in education and has earned the College of Engineering’s Teaching Excellence Award and the UIUC Campus Award for Excellence in Undergraduate Education. He has been active in the ASME, the IEEE, and several other societies. Additionally, has been active on several boards including the Scientific Advisory Board for the U.S. Air Force.  Further information may be found at: http://arg.mechse.illinois.edu/

Wednesday, April 17, 2013 - 11:30am | Hudson 208
Steve Vogel, Duke