Seminar: Negative Stiffness: Vibration damping, impact isolation, and elastic wave control
Recent advances in micro-, nano-, and additive manufacturing technology have opened the door to the development of engineered materials and structures demonstrating exotic dynamic mechanical behavior that enable elastic wave cloaking, negative refraction, and super-resolution. The same research has also reinvigorated research addressing long-standing engineering challenges such as the ability to control unwanted noise and vibration. This work presents a novel class of engineered structures with significant promise to improve vibration damping and isolation treatments, impact isolation technology, and elastic wave manipulation: negative stiffness (NS) elements. A mechanical system displaying negative stiffness is characterized by a loading state that requires a decreasing force level to increase the deformation of the system. Systems displaying NS will possess regions of negative curvature in their strain energy response as a function of deformation, hence they are unstable when unconstrained. Analytical and experimental results will be presented demonstrating that NS systems comprised of buckled beams in parallel with positive stiffness springs can be used to construct quasi-zero stiffness vibration isolation systems which provide high static but low dynamic stiffness for compact base isolation design. Transmissibility measurements of these same systems show that the nonlinearity of NS systems constructed from buckled beam structures enable tunable vibration isolation behavior and isolation from impact. Modeling results will be presented demonstrating that sub-wavelength NS elements embedded in a viscoelastic material can be used to design vibration damping treatments with increased loss factor and minimally reduced stiffness to reduce the ring-down time for an impulsively loaded multi-layered beam. Finally, numerical investigations on the use of NS honeycomb structures as tunable elastic wave manipulation will be presented.
About the Speaker
Dr. Haberman is an Assistant Professor in the Department of Mechanical Engineering at the University of Texas (UT) at Austin with a joint appointment at the Applied Research Laboratories UT Austin. He received his Ph.D. and Master of Science degrees in Mechanical Engineering from the Georgia Institute of Technology in 2007 and 2001, respectively, and received a Diplôme de Doctorat in Engineering Mechanics from the Université de Lorraine in Metz, France in 2006. His undergraduate work in Mechanical Engineering was done at the University of Idaho, where he received a B.S. in 2000. Dr. Haberman’s research interests are centered on elastic and acoustic wave propagation in complex media, acoustic metamaterials, new acoustic transduction materials, ultrasonic nondestructive testing, and vibro-acoustic transducers. He has worked extensively on the modeling and characterization of composite materials and the multi-objective design of acoustical materials. His current research focuses on modeling, design, and testing of composite materials, metamaterials, and structures for applications areas that include the absorption and isolation of acoustical, vibrational, and impulsive energy using negative stiffness structures, acoustic cloaking, and non-reciprocal acoustic and elastic wave phenomena. His work has been featured in Physics Today, Scientific American, NBC News, and National Public Radio.
Hosted by Professor Ryan Harne
Seminar: Design of Complex Vehicle Structures for Crashworthiness
For more than a decade, there have been various attempts to improve motor vehicle safety by designing complex crashworthy structures using topology optimization methods. For mildly nonlinear problems, investigators have relied on simplifications of the dynamic multi-body interaction and the structure’s nonlinear behavior to approximate sensitivity coefficients. That approach has been shown to be of limited use in large-scale, industrial applications. This research proposes a new design algorithm inspired in the distributed control mechanisms that govern biological functional adaptation—or the means by which biological structures become better suited to their environment. In this numerical approach, sensor and actuator are distributed throughout a prescribed design domain using cellular automata (CAs). A desired global structural response is achieved by design rules that locally modify the material distribution around each CA. The results obtained by the CA-based design algorithm are complex structures that show a dramatic improvement with respect to traditional topology optimization. Further improvement is also achieved through the introduction of a design and analysis of computer experiments (DACE) method. Results are demonstrated in the design of various lightweight, energy-absorbing vehicle including progressively folding thin-walled structures.
About the Speaker
Andres Tovar, Ph.D. is an Assistant Professor of Mechanical Engineering and Adjunct Assistant Professor of Biomedical Engineering at IUPUI (2011-Present). He served as a Research Assistant Professor of Aerospace and Mechanical Engineering at the University of Notre Dame (2008-2011) and as an Associate Professor of Mechanical and Mechatronic Engineering at the National University of Colombia. Dr. Tovar received his B.S. in Mechanical Engineering and M.S. in Industrial Automation from the National University in 1995 and 2000, respectively. He earned his M.S. and Ph.D. in Mechanical Engineering from the University of Notre Dame in 2004 and 2005, respectively. Currently, Dr. Tovar is the director of the Engineering Design Research Lab and the Center for Additive Manufacturing Research at IUPUI. His main research areas include simulation-based design methodologies for large-scale, nonlinear applications in materials and mechanical components.
Hosted by Professor Jami Shah
Seminar: Realistic and Intuitive Haptic Feedback for Communication in Virtual and Real-World Environments
The haptic sensations felt when interacting with the physical world create a rich and varied impression of objects and their environment. Humans are capable of gathering a significant amount of information through touch with their environment, allowing them to assess object properties and qualities, dexterously handle objects, and communicate social cues and emotions. Humans are spending a significant more amount of time in the digital world, however, and are increasingly interacting with people and objects through a digital medium. Unfortunately, digital interactions remain unsatisfying and limited, representing the human as having only two sensory inputs: visual and auditory.
This talk will focus on the investigation of haptic devices and rendering algorithms to provide humans with a touch information when communicating through a computer. I will present a background on the sense of touch, and illustrate how we can leverage this knowledge in order to design haptic devices and rendering systems that allow the human to communicate through the digital world in a natural and intuitive way. I will highlight contributions I have made in furthering haptic realism in virtual reality through the creation of highly realistic virtual objects. These objects are created by modeling high-frequency acceleration, force, and speed data recorded during physical interactions and displaying the appropriate haptic signals during rendering. I will then describe advances I have made in novel wearable haptic devices for communicating information to a human using intuitive and natural cues.
About the Speaker
Heather Culbertson is a Postdoctoral Research Fellow in the Department of Mechanical Engineering at Stanford University where she works in the Collaborative Haptics and Robotics in Medicine (CHARM) Lab. She received her PhD in the Department of Mechanical Engineering and Applied Mechanics (MEAM) at the University of Pennsylvania in 2015 working in the Haptics Group, part of the General Robotics, Automation, Sensing and Perception (GRASP) Laboratory. She completed a Masters in MEAM at the University of Pennsylvania in May of 2013, and earned a BS degree in mechanical engineering at the University of Nevada, Reno in 2010.
Hosted by Professor David Hoelzle
Seminar: Development of RANS-Based Noise Prediction Method
Computational Aero-Acoustics (CAA) methods are designed to simulate noise generation from complex flows. However, unsteady CAA computations are too time-demanding to be used for low noise design and optimization. It would be very valuable to develop much more efficient RANS-based noise prediction methods, which can also account for complex configurations and mean-flow effects. In this seminar, the key technical issues including noise source modelling, adjoint Green’s function computation and mean-flow simulation will be discussed. Several examples including jet noise, slat noise and airfoil turbulent boundary layer trailing edge noise will be presented to show the feasibility and accuracy of the developed RANS-based prediction method.
About the Speaker
Dr. Xiaodong Li is a professor of the School of Energy and Power Engineering in Beihang University (BUAA). He obtained his PhD degree from Beihang University in 1995. His interests cover computational aeroacoustics, physics-based noise prediction method and advanced measurement technology. He was a guest scientist at German Aerospace Center (DLR) in 1997 and subsequently established long-term international collaborations with several universities in Europe and USA. Now he is an international member of the Aeroacoustics Technical Committee and an Associate Fellow of AIAA. He also serves on the Editorial Board of the International Journal of Aeroacoustics.
Hosted by Professor Mei Zhuang
Seminar: Plasma Interaction with Cell-Containing Liquid – What is Important Physics?
Transport of active species in non-equilibrium plasma into a downstream aqueous sample represents an important research topic with significant application opportunities. When well controlled, reactive plasma species are capable of eradicating pathogens or cancer cells without undue damages to healthy tissues, thus offering a novel physics-based strategy to combat some of the greatest threats to human health (e.g. hospital-acquired infections). As a therapeutic intervention, plasma becomes a drug and as dug its dose must be understood and quantitatively controlled. What does this mean for plasma physics in terms of detection, control, and indeed new knowledge that may catalyze a successful translation of the gas plasma technology for health care? It is known that many biological effects of gas plasmas are facilitated mostly by reactive plasma species such as 1O2, O2-, OH and NO and some of these reactive oxygen species (ROS) can permeate into the cell to directly regulate the functions and indeed the fate of the cell. However, it is not clear which plasma-produced extracellular ROS can make into the cell and indeed which gaseous ROS make it to the liquid bulk in adequate concentrations. Starting from the endpoint of a useful technology for health care, this seminar discusses the challenges to plasma physics from some of the key knowledge gaps, through the need for new diagnostics and simulation tools, to opportunities for plasma physics to advance its scientific and technological frontiers by embracing capabilities of other disciplines.
Hosted by Professor Igor Adamovich
Seminar: Design and Pre-Processing Computational Tools for Additive Manufacturing
Additive Manufacturing (AM) has initiated a paradigm shift in the design and manufacturing approaches and has opened a whole new field of study for scientists, researchers and engineers. Although AM provides ultimate design freedom, issues specific to the manufacturability and process need to be addressed for seamless workflow that can eventually result in quality builds. This talk will present the results of the work at the Center for Global Design and Manufacturing (CGDM) at the University of Cincinnati on the development of design and preprocessing tools based on computational geometric algorithms, optimization and physics based modeling tools for powder bed based Additive Manufacturing. The presentation will include approaches for integration of topology optimization with design for additive tools, lattice structures, geometric compensation approaches, optimization of input file, slicing and build orientation for achieving part tolerances as well as minimizing and optimal removal of support structures.
About the Speaker
Sam Anand is a Professor of Mechanical Engineering and Director of Center for Global Design and Manufacturing at the University of Cincinnati. He also serves as the Director of UC/Siemens Simulation Center and Co-Director of UCRI Advanced Manufacturing Center. He obtained his MS and PhD in Industrial Engineering from Penn State University. Prof. Anand’s areas of research expertise include Intelligent Product Design, Precision Engineering, Virtual Modeling, Simulation and Optimization of Additive and Subtractive Manufacturing Processes. He has graduated 65 MS and 9 PhD students, published over 100 technical papers and received in excess of $10M in research grants and contracts in his research areas from Federal and State agencies as well as Industries. He currently serves as an Associate Editor of ASME Journal of Manufacturing Science and Engineering and has previously served as Associate Editor of SME Journal of Manufacturing Systems.
Hosted by Professor Jami Shah
Seminar: Florin Bobaru
Material damage induced by corrosion can trigger sudden failure of structures by introducing pits that act as stress concentration points from which cracks initiate and propagate catastrophically. Many materials are also susceptible to Stress Corrosion Cracking (SCC) in which changes introduced in the material by corrosion processes dramatically reduce its fracture toughness. This talk will present our efforts on predicting the evolution of corrosion damage, pitting corrosion, and SCC, to better understand failure of materials in corrosive environments. The new models we introduced are of peridynamic type (nonlocal models) that allow for a consistent treatment of damage and cracks in a variety of forms in which they are present in corrosion processes. I will cover a recent model we introduced that is capable of simulating the passivation, salt-film formation, and the autonomous formation of lacy covers in pitting corrosion. The computational results under potentiostatic conditions are in excellent agreement with experiments in both time-scale and length-scale. The model is also used to investigate the effect stresses have on corrosion rates, and SCC. I will give a brief account on why peridynamic modeling of fracture, damage, fragmentation is useful.
About the Speaker
Prof. Bobaru obtained his Ph.D. in Theoretical and Applied Mechanics from Cornell University in 2001. He holds B.S. (1995) and M.S. (1997) degrees in Mathematics and Mechanics of Solids from University of Bucharest. He joined University of Nebraska-Lincoln as Assistant Professor in 2001, where he has been Full Professor of Mechanical and Materials Engineering since 2013. Prof. Bobaru has had Visiting Scholar appointments at Sandia National Laboratories (2002-2005, 2009), at Cambridge University (2008), at California Institute of Technology (2011), at University of Padova (2015), and at University of Texas at Austin (2015). He has published extensively on peridynamic modeling of dynamic fracture and failure and he introduced peridynamic models for heat flow in bodies with evolving discontinuities and corrosion damage. Other publications include shape and material optimization, and dynamics of granular materials. He is the main editor of the recently published “Handbook of Peridynamic Modeling”.
Hosted by Professor Soheil Soghrati
Seminar: Vibration Analysis of Spinning Rotors with Flexible Bearings and Housing Supports
Rotary machines appear everywhere in our daily life ranging from jet engines to computer hard disk drives. Every rotary machine consists of three basic elements: a rotary part (rotor), a stationary part (housing), and multiple bearings that connect the rotary and stationary parts. The rotor can be axisymmetric (e.g., hard disk drives) or cyclic symmetric (e.g., wind turbines).
In this presentation, we will discuss how bearings and housing affect vibration of a spinning rotor. Mathematical models are developed through use of Lagrange equation, finite element analyses and component mode synthesis. The mathematical modeling leads to the following conclusions. First, when a rotor is assembled to housing via bearings, some vibration modes will not change their natural frequencies and mode shapes. These modes have the characteristics of zero inertia force and inertia moment. Therefore, they are called “balanced modes.” Otherwise, a vibration mode is called an “unbalanced mode.” Only unbalanced modes will be coupled to the housing and bearings. Second, for axisymmetric rotors, unbalanced modes will appear in the form of precession or axial translation when they are coupled with the housing and bearings. In the case of hard disk drives, one-nodal-diameter disk modes present precession and axisymmetric disk mode present axial translation. Disk modes with 2 or more nodal diameters are balanced modes. Third, for cyclic symmetric rotors, balanced or unbalanced modes will depend on the number of repeated substructures and a “phase index” , which determines the phase angle between two neighboring substructures. A vibration mode is a balanced mode if , , or . Finally, when mistuning is present in a cyclic symmetric rotor, localized vibration modes may appear. Presence of bearings may introduce more localized modes and may couple the housing to the rotor. Localized modes are unbalanced with larger bearing forces.
Majority of the mathematical predictions have been validated via calibrated experiments.
About the Speaker
Professor Steve Shen received his B.S. and M.S. degrees from National Taiwan University and Ph.D. from the University of California (Berkeley), both in Mechanical Engineering. Professor Shen’s general research area is vibration, dynamics, sensing, and actuation. In particular, his expertise includes PZT thin-film micro-sensors/actuators, flapping-wing micro aerial vehicles, medical devices (hearing and dental implants), and spindle and rotor dynamics.
Professor Shen is a Fellow of American Society of Mechanical Engineers (ASME). He is currently the Technical Editor of ASME Journal of Vibration and Acoustics. Professor Shen is a recipient of ASME N. O. Myklestad Award and IBM Partnership Award.
Hosted by Professor Kiran D’Souza
Seminar: New Solution Paradigms for Uncertainty Forecasting in High-Dimensional Nonlinear Stochastic Systems
In this talk, we will look at a snapshot of the new Laboratory for Autonomy in Data Driven and Complex Systems (LADDCS) at the Aerospace Research Center (ARC). LADDCS focuses on theoretical and computational research in uncertainty characterization, forecasting and fusion, as well as control of uncertain (better known as stochastic) systems. Challenges associated with the Fokker-Planck equation (FPE), a holy grail problem in stochastic dynamics will be discussed. Two fundamentally distinct solution paradigms will be presented – i.) tensor-based discretization, and, ii.) adaptive particle discretization in the framework of Monte Carlo methods. The key objective of both classes of methods is to accurately capture non-Gaussianity while alleviating the curse of dimensionality. We will present our results in a wide variety of fields, including weather-forecasting, space-situational awareness and the modeling of polymeric fluids.
About the Speaker
Dr. Mrinal Kumar received a Ph.D. in 2009 from Texas A&M University and a Bachelor’s degree in 2004 from the Indian Institute of Technology, Kanpur, both in aerospace engineering. Before joining OSU in Fall 2016 as an Associate Professor in the MAE department, he was an Assistant Professor in the same department at the University of Florida. At OSU, Dr. Kumar founded the Laboratory for Autonomy in Data-Driven and Complex Systems (LADDCS), which is home to research in nonlinear stochastic dynamical systems, Fokker‐Planck equations, Markov‐chain Monte Carlo methods, stochastic optimization and chance-constrained optimization and control. He received the Best Paper of Conference Award at the 2006 Astrodynamics Specialist Conference, the 2007 AIAA Open Topic Graduate Research Award, and more recently, the NSF CAREER Award in 2013 and the AFOSR Young Investigator Award in 2015.
Affiliation: University of Michigan
Hosted By: Professor Bharat Bhushan
Description: In this talk I will discuss the current work in my group on developing surfaces with extreme wettabilities, i.e. surfaces that are either completely wet by, or completely repel, different liquids. The first portion of the talk will cover the design of so called “superomniphobic surfaces” i.e. surfaces which repel all liquids. Designing and producing textured surfaces that can resist wetting by low surface tension liquids such as various oils or alcohols has been a significant challenge in materials science, and no examples of such surfaces exist in nature. As part of this work, I explain how re-entrant surface curvature, in addition to surface chemistry and roughness, can be used to design surfaces that cause virtually all liquids, including oils, alcohols, water, concentrated organic and inorganic acids, bases, solvents, as well as, viscoelastic polymer solutions to roll-off and bounce.
The second portion of my talk will cover the design of the first-ever reconfigurable membranes that, counter-intuitively, are both superhydrophilic (i.e., water contact angles @ 0°) and superoleophobic (i.e., oil contact angles > 150°). This makes these porous surfaces ideal for gravity-based separation of oil and water as they allow the higher density liquid (water) to flow through while retaining the lower density liquid (oil). These fouling-resistant membranes can separate, for the first time, a range of different oil–water mixtures, including emulsions, in a single-unit operation, with >99.9% separation efficiency, by using the difference in capillary forces acting on the oil and water phases. As the separation methodology is solely gravity-driven, it is expected to be one of the most energy-efficient technologies for oil-water separation.
I will also discuss surfaces with patterned wettability, where both wetting (omniphilic) and non-wetting (omniphobic) domains are fabricated on the same substrate. We use such substrates for fabricating monodisperse, multi-phasic, micro- and nano-particles possessing virtually any desired composition, projected shape, modulus, and dimensions as small as 25 nm. Finally, I will discuss some other areas of current and future research, including the development of ice-phobic coatings that offer one of the lowest reported adhesion strengths with ice.