Conferences, Lectures, & Seminars
Events for February
-
AME Department Seminar
Wed, Feb 01, 2012 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Speaker: Sergio Pellegrino, Graduate Aerospace Laboratories. California Institute of Technology. Pasadena, CA
Talk Title: Multiple Equilibria of Inflatable Structures
Abstract: The shape of inflatable structures is determined by overall energy considerations coupled with the unilateral constraints imposed by their envelope (which is unable to carry compression) and by frictional self-contact. These ingredients lead to the existence of multiple equilibrium configurations, however our everyday experience with inflatable structures leads us to assume uniqueness. We tend to associate alternative equilibrium shapes with clearly anomalous deployment. Thus, the observation of large S-clefts during test flights of NASA superpressure balloons was initially attributed to some of kind of deployment anomaly, as these counterintuitive equilibrium shapes had not been seen before and could not be explained without first understanding the shape of clefted balloons. In this talk I will review some experiments that have confirmed the initial flight test observations and I will present an analysis that captures key aspects of the evolution of clefting during deployment and leads to S-clefts that closely resemble those seen in the experiments.
Host: Prof. Udwadia
More Info: http://ae-www.usc.edu/seminars/index.shtml#upcomingLocation: Seaver Science Library (SSL) - 150
Audiences: Everyone Is Invited
Contact: April Mundy
Event Link: http://ae-www.usc.edu/seminars/index.shtml#upcoming
-
AME Seminar
Wed, Feb 08, 2012 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Speaker: Tamar Shinar, Amrik Singh Poonian Assistant Professor; Computer Science & Engineering Department, University of California, Riverside, Riverside, CA
Talk Title: A Computational Model of Microtubule-Based Motion in the Single-Celled C. elegans Embryo
Abstract: We develop a simple model of microtubule-based pronuclear motion in a single-celled C. elegans embryo. The model consists of a model for microtubule dynamic instability, a Newtonian, viscous fluid contained within an enclosing geometry for the cytoplasm, a rigid body for the pronucleus, and a motor protein load-velocity relationship. Motor proteins distributed throughout the cytoplasm interact with microtubule filaments by sliding along them with a velocity that depends on their load. They in turn pull on the filaments, resulting in translation of the microtubule-bound pronucleus. Our simulations show pronuclear migration, and moreover, a robust pronuclear centration and rotation very similar to that observed in vivo. I will also describe the numerical method for the coupled simulation of the Stokes fluid and rigid structures.
Host: Dr. Paul Newton
Location: Seaver Science Library (SSL) - 150
Audiences: Everyone Is Invited
Contact: April Mundy
-
AME Department Seminar
Wed, Feb 15, 2012 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Speaker: L. Lamberson, Postdoctoral Research Scholar at the Center for Advanced Metallic and Ceramic Systems. Johns Hopkins University.
Talk Title: Cracks, Dynamics & the Piezoelectric Effect
Abstract: While a large amount of data is available on the properties and behavior of piezoelectric ceramics subjected to small strains and electric fields as used in conventional sensor and actuator applications, little data exists which contributes to a basic understanding of the behavior of piezoelectric ceramics subjected to high-rate impulsive loading. This particular loading regime plays a critical role in defense applications, specifically for blast mitigation and ballistic protection since numerous armor ceramics such as silicon carbide and aluminum nitride exhibit piezoelectric properties. In addition, piezoelectric materials are also valued for their ability to be utilized as a single-shot, high-energy power supply (or switch) when pulverized, as well as in energy resource recovery applications. In order to utilize these materials âsmartâ ability, the frequency-time response plays a crucial role in failure, and depends on both the mechanism of polarization, as well as the effect of damage on polarization.
This talk focuses on high strain rate dynamic electromechanical experiments (103 s-1) conducted on single crystal α-quartz, single crystal silicon carbide and aluminum nitride. The results exhibit unexpected trends stress-charge behavior during damage evolution. Specifically, when quartz is undergoing extensive and irreversible dynamic brittle fracture under a compressive stress impulse of up to 2 GPa, the effective piezoelectric stress coefficient increases from loading to unloading. The experimental results are examined in the framework of the theory of linear piezoelectricity and compared to traditional continuum damage models, in order to understand the role of increasing crack density on electroelastic properties.
Biography: Dr. Leslie Lamberson has an appointment as an Assistant Professor in the Mechanical Engineering and Mechanics Department at Drexel University, and is presently a Postdoctoral Research Scholar at the Center for Advanced Metallic and Ceramic Systems at the Johns Hopkins University. Her research encompasses high strain rate material system behavior. Leslie received her BS in Aerospace Engineering from the University of Michigan, and MS in the same discipline from the Georgia Institute of Technology. Working with Professor Ares Rosakis, she completed her Ph.D. in Aeronautics from the California Institute of Technology examining hypervelocity impact induced dynamic fracture behavior of brittle polymers.
Host: Professor Veronica Eliasson
More Info: http://ae-www.usc.edu/seminars/index.shtml#upcomingLocation: Seaver Science Library (SSL) - 150
Audiences: Everyone Is Invited
Contact: April Mundy
Event Link: http://ae-www.usc.edu/seminars/index.shtml#upcoming
-
AME Department Seminar
Wed, Feb 22, 2012 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Speaker: Mukul Kumar , Staff Scientist. Physical & Life Sciences Directorate. Lawrence Livermore National Laboratory. Livermore, CA 94550.
Talk Title: Grain Boundary Networks: From Consideration of the Individual Constituents to the Collective Response
Abstract: It has been demonstrated that mechanical response, particularly environmental degradation, of FCC metals and alloys can be improved by exercising control over the population of grain boundary types in the microstructure. The studies also suggest that such properties tend to have percolative mechanisms that depend on the topology of the grain boundary network. Grain boundary engineering investigations have been facilitated by the emergence of SEM-based automated electron backscatter diffraction (EBSD) that enables the characterization of statistically significant datasets of interface crystallography. The EBSD datasets have been analyzed to quantify microstructures in terms of grain boundary character and triple junction distributions. Perhaps more significantly, these large datasets also enable us to visualize crystallographically correlated domains of multiple grains that have been shown to strongly influence crack propagation through the microstructure. Examples from studies on hydrogen and weld embrittlement, stress corrosion cracking, and fatigue will be presented to demonstrate these points along with the constitutive response of such microstructures.
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Biography: Mukul Kumar is a Staff Scientist in the Physical & Life Sciences Directorate at LLNL. Prior to joining LLNL, he received his PhD from the University of Cincinnati and had a stint as a postdoctoral fellow at Johns Hopkins University. His research activities have revolved around correlating microstructures with the macroscopic response of the material. This has involved diverse conditions such as travelling strong shock waves to challenging environments seen in jet engines and nuclear reactors. There is growing involvement in taking the next step of formulating predictive models for materials behavior, particularly damage and fracture, and translating them into processing routes for optimized microstructures.
Host: Prof. Andrea Hodge
More Info: http://ae-www.usc.edu/seminars/index.shtml#upcomingLocation: Seaver Science Library (SSL) - 150
Audiences: Everyone Is Invited
Contact: April Mundy
Event Link: http://ae-www.usc.edu/seminars/index.shtml#upcoming
-
AME Department Seminar
Wed, Feb 29, 2012 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Speaker: Anders Petersson, Center for Applied Scientific Computing. Lawrence Livermore National Laboratory. Livermore, CA.
Talk Title: Source Estimation by Full Wave Form Inversion
Abstract: We discuss the inverse problem of determining the source parameters of a small seismic event (location, mechanism, start time, frequency), such that the wave form misfit between seismographic recordings and simulated ground motions is minimized. Our approach is based on direct numerical simulations of the elastic wave equation, allowing for complex heterogeneous material models and realistic topography. A non-linear conjugated gradient approach is applied to solve the inverse problem, where the gradient of the misfit (with respect to the source parameters) is calculated from the numerical solution of an adjoint wave equation. Numerical experiments on simple 2-D models illustrate the importance of scaling the source parameters before applying the conjugated gradient iteration, preferably using the Hessian. A procedure based on arrival times is used to generate an initial guess for the source parameters. For the cases considered here, the conjugate gradient iteration often converges in 20-50 iterations.
Solving the inverse problem requires of the order O(100) numerical solutions of the elastic wave equation. For 3-D models, such problems can only be solved on large parallel machines. We will present the capabilities of our parallel open source code WPP, which was designed to solve seismic wave propagation problems on the regional scale. A higher order accurate scheme is currently being implemented to improve the the frequency resolution and efficiency of the method. These enhancements will be important for solving the three-dimensional inverse problem, for example in geothermal applications where there is interest in using micro seismicity for imaging the geometry of a fractured network.
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. This is contribution LLNL-ABS-523199.
Host: Prof. Veronica Eliasson
More Info: http://ae-www.usc.edu/seminars/index.shtml#upcomingLocation: Seaver Science Library (SSL) - 150
Audiences: Everyone Is Invited
Contact: April Mundy
Event Link: http://ae-www.usc.edu/seminars/index.shtml#upcoming