MEAM Seminar Series Summer 2017

For Spring 2017 Seminars, click here.

Seminars are held on Tuesday mornings beginning at 10:45 am in Room 337, in the Towne Building (unless otherwise noted).

To be added to the MEAM Events mailing list (which sends notifications regarding all departmental seminars and events) please email us at meam-events@lists.seas.upenn.edu.

June 6

Seok Kim, Assistant Professor, Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign

"Transfer Printing for LEGO-like Microassembly and Nanomaterial Integration"

Abstract:

Reversible dry adhesion-based transfer printing provides a highly straightforward pathway to heterogeneous material integration. The speaker presents his recent research outcomes accomplished in his laboratory which has been exploring responsive surfaces, microassembly, and nanomanufacturing technologies. The first part introduces an engineered reversible dry adhesive made of a shape memory polymer and highlights its consumer product-like prototype. The second part shows how his reversible dry adhesive advances transfer printing techniques to enable his microassemly method called micro-LEGO and summarizes the applications of micro-LEGO with the examples not only of 3D heterogeneous micro-structures but also of devices such as a microtoroid resonator, a tip-tilt-piston micromirror, and a RF MEMS switch. Finally, the third part demonstrates his transfer printing techniques to be further exploited in order to pattern and integrate colloidal quantum dot films. The strategies presented in his talk benefit research activities in smart dry adhesives, 3D MEMS, and nano devices.

Bio:

Seok Kim received his B.S. from Pohang University of Science and Technology, M.S. from University of California at Los Angeles, and Ph.D. from Carnegie Mellon University, all in mechanical engineering, and joined the faculty at the University of Illinois at Urbana-Champaign in 2011. His current research interests include biomimetic design of responsive surfaces for reversible dry adhesion and tunable wetting, transfer printing-based microassembly and nanomanufacturing, and 3D MEMS fabrication technologies. He was a recipient of the National Science Foundation CAREER Award in 2014, the ASME Chao and Trigger Young Manufacturing Engineer Award in 2015, and the Young Investigator Grant Award from the Korean–American Scientists and Engineers Association in 2015.


June 13

PhD Seminar
Paul Barclay
, PhD Candidate, University of Pennsylvania
Advisor: Jennifer Lukes

"Molecular Dynamic Study on Fluid Flow and the Fluid-Fluid Interfacial Mobility"

10:45 am, Towne 337

Abstract:

A nonequilibrium molecular dynamics method to induce fluid flow in nanochannels, the insertion-deletion method (IDM), is introduced. IDM inserts and deletes particles within distinct regions in the domain, creating locally high and low pressures. The benefits of IDM are that it directly controls a physically meaningful quantity, the mass flow rate, allows for pressure and density gradients to develop in the direction of flow, and permits treatment of complex aperiodic geometries. Validation of IDM is performed, yielding good agreement with the analytical solution of Poiseuille flow in a planar channel. Comparison of IDM to existing methods indicates that it is best suited for gases, both because it intrinsically accounts for compressibility effects on the flow and because the computational cost of particle insertion is lowest for low-density fluids.

Dual control volume grand canonical molecular dynamics is used to calculate fluid-fluid interfacial mobility from random interface walks. The mobility is calculated from one-dimensional walks of the interface with no driving force by using the fluctuation-dissipation relation similar to the Stokes-Einstein relation. The mobility is calculated with the interfacial mean square displacement as well as with the interfacial velocity autocorrelation function. One liquid-vapor and two liquid-liquid interfaces are simulated to examine the robustness of this method.


June 15

PhD Defense
Ting Yue, Ph.D. Candidate, University of Pennsylvania
Advisor: Noam Lior

"Thermodynamic Analysis for Improving Uunderstanding and Performance of Hybrid Power Cycles Using Multiple Heat Sources of Different Temperatures"

3:00 p.m., Room 227, Towne Building

Abstract:

Past studies on hybrid power cycles using multiple heat sources of different temperatures focused mainly on case studies and almost no general theory about this type of systems has been developed. This dissertation is a study of their general thermodynamic performance, with comparisons to their corresponding single heat source reference systems. The method used in the dissertation was step-wise: to first analyze the major hybrid power cycles (e.g. Rankine, Brayton, Combined Cycles, and their main variants) thermodynamically, without involving specific operation parameter values, and develop some generalized theory that is at least applicable to each type of system. The second step was to look for commonalities between these theories and develop the sought generalized theory based on these commonalities. A number of simulation case studies were performed to help the understanding and confirm the thermodynamic results. Exergo-economic analysis was also performed to complement the thermodynamic analysis with consideration of externalities, and was compared to the conventional economic analysis method. The generalized expressions for the energy/exergy efficiency differences between the hybrid and the corresponding single heat source systems were developed. The results showed that the energy and exergy efficiencies of the hybrid systems are higher than those of their corresponding single heat source reference systems if and only if the energy/exergy conversion efficiency (defined in the dissertation) of the additional heat source (AHS, can be any heat source that has lower temperature) is larger than that of the original heat source. Sensitivity analysis results showed the relations between the temperature and heat addition rate of the AHS and the energy/exergy efficiency of the hybrid systems. Other big advantages of hybrid systems, i.e. the effects on replacement of fossil fuel by renewable, nuclear and waste energy, lower emissions and depletion of fossil fuel, were revealed in the economic analysis, by considering the cost reduction from fuel saving and carbon tax. Simple criteria were developed to help compare the hybrid and reference systems and determine under which conditions the hybrid systems will have better thermodynamic or economic performance than the reference ones. The results and criteria can be used to help design the hybrid systems to achieve higher energy and/or exergy efficiencies and/or lower levelized electricity cost (LEC) before detailed design or simulation or experiment. So far, 3 archival journal papers and 3 conference papers were published from this dissertation work.


June 20

PhD Seminar
James Hilbert, PhD Candidate, University of Pennsylvania
Advisor: Robert Carpick

"Carbon coatings under extreme conditions: Understanding and addressing the thermal instability and humidity-dependent tribology of hydrogenated amorphous carbon films by using silicon and oxygen as dopants"

10:45 am, Towne 337

Abstract:

Hydrogenated amorphous carbon (a-C:H) films are amorphous materials made of hydrogen and carbon bonded in both sp2 and sp3 configurations. These films are notable for their high hardness (10-16 GPa, compared to 1-1.5 GPa for steel), ease of application to a wide range of substrates, and good tribological performance (low friction and wear). However, they suffer from significant limitations. First, a-C:H becomes unstable above 150°C, preventing its use in important technological applications, such as heat assisted magnetic recording (HAMR) disk drives. Second, the low friction and wear is only maintained in dry and vacuum conditions. This prevents their use as protective coatings in applications where the humidity may vary such as use in aerospace components which need to function in and outside the atmosphere.

To understand and potentially address these limitations, we consider the effect of adding silicon and oxygen to a-C:H films, since prior experimental evidence shows that this can significantly increases thermal stability, and help maintain low friction and wear when sliding in humid environments. However, the mechanisms for these improvements are unknown.

Reactive molecular dynamics (MD) simulations using the ReaxFF potential were performed on undoped a-C:H and a-C:H doped with Si and O (a-C:H:Si:O) to explore the effect on thermal stability. Atomistic thermal degradation pathways were examined to understand the origins of the enhanced thermal stability endowed by SiOx-doping. As in experiments, the simulated a-C:H:Si:O demonstrated increased thermal stability compared to conventional a-C:H. The primary thermal degradation pathway in undoped a-C:H was observed to be the breaking of tensile strained C-C bonds resulting in a transformation of sp3 to sp2-hybridized carbon. The presence of Si suppresses this mechanism by decreasing the frequency of highly strained C-C bonds in the unannealed structure. This is due to the longer C-Si equilibrium bond length compared to C-C bonds, which allows the Si-doped films to accommodate higher structural disorder.

To explore the improvement in the tribological properties, we measured coefficients of friction varying from approximately 0.05 in dry environments (RH < 5%) to 0.15 in humid air when sliding against steel, significantly better than prior observations for undoped a-C:H films. The wear rate is also environmentally-dependent and typically correlated with friction. The friction and wear behavior is controlled by the formation of adhesive junctions between the a-C:H:Si:O films and the steel balls. Possible mechanisms underlying this behavior will be discussed.


June 27

PhD Seminar
Chenchen Liu, PhD Candidate, University of Pennsylvania
Advisor: Celia Reina

"Multiscale Modeling and Design of Acoustic Metamaterials"

10:45 am, Towne 337

Abstract:

Elastic composite/metamaterials have exhibited a rapid increase of interest due to their surprising dynamic properties, such as sub-wavelength band gaps, negative effective elastic constant and/or density and frequency-dependent elastic anisotropies. The design and optimization of these novel materials architectures call for an enhanced understanding of the microstructure-properties relations when micro-inertia effects may start to play a macroscopically observable role.

In this talk, we present a variational coarse-graining framework for heterogeneous media, that allows for a seamless transition from the traditional static scenario to dynamic loading conditions, while being applicable to general material behavior as well as to discrete or continuous representations of the material and its deformation, e.g., finite element discretizations or atomistic systems. The method automatically delivers the macroscopic equations of motion, which are in general not in closed form, together with the generalization of Hill's averaging relations to the dynamic setting. We further demonstrate with a proof of concept example, that the proposed theoretical framework can be used to perform multiscale numerical simulations in the spirit of FE2 methods. The results are compared with standard single-scale finite element simulations, showcasing the capability of the method to capture the dispersive nature of the medium in the range of frequencies permitted by the multiscale strategy.

We further present material architecture designs based on resonant hierarchical structures. These systems are promising to generate multiple band gaps thanks to their inherent multiple scales, and are here investigated systematically as a function of the relevant parameters in idealized lattice systems. Based on these results, we propose graded hierarchical designs that deliver phononic crystals with enhanced bandwidth. These theoretical analyses based on lattice system are then certified using continuum models and finite element simulations.


July 4

Independence Day - NO SEMINAR


July 11

Ruiyuan Ma


July 18

PhD Seminar
Mohammed Asaduzzaman, PhD Candidate, University of Pennsylvania
Advisor: Howard Hu

"Interfacial Wave Dynamics of Core-Annular Flow of Two Fluids"

10:45 am, Towne 305

Abstract:

In Core-Annular flow of two different fluids, for a set of suitable flow conditions, various shapes of saturated waves such as Bamboo waves, Snakes, and Cork-Screw waves are observed. Some of the dominant parameters such as thickness ratio of the fluid, Reynolds number, viscosity ratio, density ratio, interfacial surface tension, and the direction of gravitational forces determine the final shape of the saturated wave and their ultimate stability in a non-linear regime.

When the flow rate ratio is high, sometimes it is difficult to determine the differences between the final shape of the waves for up-flow and down-flow. For some combinations of thickness ratio, viscosity ratio, density ratio, Reynolds number and surface tension, waves tend to break down and a bubble starts to form. Interfacial surface tensions between these two fluids play a very important role to stabilize the waves from breaking down.

In this study, new sets of waves were discovered for core-annular flow, which modulate at certain flow parameter ranges. The critical parameter ranges are identified where the waves shift from saturated non-modulated wave and bifurcate into saturated modulated waves. A thorough analysis is performed for the first time to depict the windows of these critical parameters at which this transition takes place. A bifurcation diagram is constructed to capture the regime. A detailed wave shape analysis is performed to characterize these wave shapes and their periods of oscillation.

Due to challenges associated with large computational domain and an enormous computational power requires to resolve the interfacial instability, a three-dimensional true non-axisymmetric model was never studied before. For the first time, effort is being undertaken to construct a viable 3-D Core-Annular flow. Computational Fluid Dynamics package ANSYS Fluent™ is used for this analysis. Three dimensional models for both Up-flow and Down-flow were constructed and a novel explanation is presented to distinguish between the Bamboo waves, Cork-Screw waves, and Snake waves. The sensitivity of down flow on initial conditions were also verified with 3-D models on some parameter space from selected publication.


July 21

(Special Seminar) Sarah Tang


July 25

Monroe Kennedy


July 28

(Special Seminar) Sikang Liu


August 1

Mickey Whitzer


August 8

Yuejun Yan


August 15

Chen Lin


August 22

Xiaoguai Li


August 29

Dawei Song