The seminar will be held on Mon Jan 28 4pm – 5pm in Guggenheim 204.
"Trends in 20th Century Northeast Pacific Storm Activity" by Adam Skalenakis, Graduate Student, Department of Atmospheric Sciences, UW, Atmospheric Sciences and Geophysics 310C.
Engineering Reference Frames in the Ocean
Monday, 5 March 2012
1:30 to 2:20 PM
Mechanical Engineering Building – Room 238
Oceanographer, Applied Physics Laboratory
Assistant Professor, Department of Civil and Environmental Engineering
University of Washington
The choice of reference frame is central to any research in fluid mechanics. In the ocean, the choice is further complicated by many practical limits in measurement platforms. This talk will present several recent applications of fixed (Eulerian) and fluid-following (Lagrangian) measurements in the ocean, and the engineering to support those measurements. Special attention will be given to the wave-following reference frame and the development of a new platform, the Surface Wave Instrument Float with Tracking (SWIFT). Measurements from the SWIFT are used to measure the turbulent cascade of energy during wave breaking, a process central to air-sea interaction and wave evolution. Details of the design, testing, and application of SWIFT will be presented as a case study in ocean engineering for ocean science.
Tuesday, March 13, at 3:30 PM in Guggenheim 218
The Airborne Laser
University of Texas at Austin
The idea of placing a large high power laser on an aircraft to shoot down ballistic missiles in the boost phase was first suggested by Dr. Edward Teller in 1967. A study led by Professor Abraham Hertzberg of the University of Washington recommended that an Airborne Laser Laboratory (ALL) be developed using a Boeing KC-135 tanker aircraft as the test bed and using a 500 KW Carbon Dioxide gas-dynamic laser. General George Brown, Commander of AFSC approved, and the program was Initiated in 1971. Extensive wind tunnel tests conducted at the NASA Ames Research Center proved the feasibility of the concept and the aircraft was modified. In May 1983, the ALL destroyed five AIM-9L missiles in flight. The program proved the concept but was then suspended because no laser of military value existed. With the advent of the Chemical Oxygen-Iodine Laser (COIL) and adaptive optics, Air Force Chief of Staff Ronald Fogleman revived the program in 1994. A Boeing 747-400 cargo aircraft was modified to carry a multi-megawatt COIL laser, which was designated the Boeing YAL-1A Airborne Laser (ABL), and was completed in 2009. The first “full up” tests were successfully conducted on February 4th and 10th, 2011. First the ABL aircraft shot down a solid-fueled “Black Brandt” missile, and on the 10th the ABL shot down a liquid fueled “SCUD-B” and acquired another “Black Brandt.” However, the laser was turned off by a safety device before the missile was destroyed. The ranges achieved by the COIL laser are classified but are of military interest. The ABL program was “suspended” in 2011 but the airplane was kept in flight status until December, when the ABL program was cancelled. It made its final flight on February 14, 2012 to Davis-Monthan AFB in Tucson, Arizone to be prepared and kept in storage at the “Boneyard.”
Biography of Hans Mark
Dr. Hans Mark specializes in the study of spacecraft and aircraft design, electromagnetic rail guns, and national defense policy. He has served on the faculty of the Department of Aerospace Engineering and Engineering Mechanics at the University of Texas., Austin, since 1988. Since 2001 he has held the John J. McKetta Centennial Energy Chair in Engineering. He served as Chancellor of The University of Texas System from 1984 to 1992. Previously, he taught at Boston University, MIT, University of California at Berkeley, and Stanford University.
Dr. Mark has also served as Director of the NASA-Ames Research Center, Secretary of the Air Force, Deputy Administrator of NASA, and more recently, Director of Defense Research and Engineering at the Pentagon. He has published numerous papers and authored or edited eight books. Dr. Mark is a member of the National Academy of Engineering and an Honorary Fellow of the AIAA. He is the recipient of the 1999 Joe J. King Engineering Achievement Award and the 1999 George E. Haddaway Medal for Achievement in Aviation. In 2006 he received the Military Astronautics Award from the American Astronautical Society. In 2007 he was bestowed the U.S. Navy’s Distinguished Public Service Award, and in 2008 he was presented the James E. Hill Lifetime Space Achievement Award by the Space Foundation. In addition, Dr. Mark has received six honorary doctorates.
Interplay between turbulence and particles in environmental flows with primary focus on turbidity currents
Department of Mechanical & Aerospace Engineering
University of Florida, Gainesville, FL
The intensity and sustained propagation of a turbidity current depends on the interplay between suspended particles and turbulence. Suspended particles drive the ﬂow and are the source of turbulence in a turbidity current, while the ﬂow turbulence enables resuspension of particles from the bed. If resuspension dominates over deposition the intensity of the current can increase, thereby further increasing resuspension and resulting in a runaway current. But stable stratiﬁcation due to suspended sediment concentration can damp and even kill turbulence. Then deposition dominates over resuspension and the current could laminarize resulting in massive deposits.
The three control parameters are the ﬂow Reynolds number, the Richardson number and the non-dimensional suspension settling velocity. In this talk we present results from direct numerical simulations of various conﬁgurations of continuous turbidity currents. The model is applied to study turbulence modulation due to changes in Richardson number and settling velocity, and its eﬀects on the transport capacity of suspended sediment. The results indicate the existence of conditions for the damping of the near-bed turbulence. Under these conditions, sediment in suspension rains out passively on the bed, even though the upper layer may remain turbulent. The above scenario provides a reasonable (but not unique) explanation for the formation of massive turbidities in scenarios of slope change of the bed or loss of lateral ﬂow conﬁnement.
The key mechanism that dictates the rate of resuspension of particles is the eﬀective hydrodynamic force that rolls/lifts the particle from the bed into the bulk. Much of the existing resuspension models are empirically driven. An essential building block to our understanding and physics-based modeling of resuspension is to consider the problem of forces on a particle in a turbulent boundary layer on a rough bed. Time permitting, our recent work in this direction will also be presented.
Professor S. ”Bala” Balachandar is currently William F. Powers professor in the Department of Mechanical & Aerospace Engineering at the University of Florida where he was chair from 2005 to 2011. Before joining University of Florida, he was a professor in the Department of Theoretical & Applied Mechanics at UIUC. Before joining University of Illinois he worked for a year at NASA Langley Research Center as a contractor. Prof. Balachandar got his BTech from Indian Institute of Technology, in 1983 Madras and his PhD from Brown University in 1989.
Professor Balachandar’s expertise is in computational multiphase ﬂow, direct and large eddy simulations of transitional and turbulent ﬂows and integrated multiphysics simulations. He is a fellow of the APS and the ASME. He received the Francois Naftali Frenkiel Award from APS-Division of Fluid Dynamics in 1996 and the Arnold O. Beckman Award and the University Scholar Award from UIUC. He was an associate editor of the ASME Journal of Fluids Engineering and currently is the associate editor of the International Journal of Multiphase Flow.
Prof. Martin Wosnik, Mechanical Engineering Department, from University of New Hampshire will be giving the ME seminar entitled “Marine Hydrokinetic Energy Conversion Research – from the Laboratory to Open Water Test Sites.”
Research related to marine hydrokinetic (MHK) energy conversion will be presented. The work spans multiple scales – related to “Technology Readiness Levels” defined by DOE – ranging from research on hydrofoil sections, to systematic evaluation of turbines and wake measurements in a large cross-section tow tank, to open water turbine deployments at a tidal energy test site. A low-drag test bed for marine hydrokinetic turbines that allows measurement of turbine rotor performance and overall thrust on the turbine was developed for an 8’ x 12’ cross-section tow tank. Studies of cross-flow axis turbines provided insights into the physical principles of operation of this class of turbines; including the effects of waves and turbulence. Turbine performance is generally enhanced by progressive waves, but waves can also cause stalling at higher tip speed ratios compared to the steady case. Grid turbulence can enable cross-flow axis turbines to operate at lower tip speed ratios while not decreasing maximum power coefficient, but increasing thrust (drag) on the turbine slightly. Performance of a cross-flow axis turbine in the wake of an upstream obstruction, e.g., in a cylinder wake is highly dependent on the cylinder’s cross-stream location, ranging from benign to detrimental. A new, highly modular and instrumented physical scale model of a Reference Vertical Axis Turbine (RVAT) is under development. A newly renovated high speed water/cavitation tunnel is used for hydrofoil research: to obtain performance data and establish cavitation criteria for uni-and bi-directional hydrofoil sections from MHK turbine blades, including the validation of cavitation inception models for MHK turbines. Open-water deployments of MHK turbines will be discussed, including cross-flow axis and un-ducted and ducted in-stream axis turbine configurations.
A brief overview of the test sites and physical infrastructure at UNH-CORE will be given. CORE’s physical infrastructure is unique in terms of proximity, ease of access, and favorable test site characteristics. It consists of the Chase Ocean Engineering (OE) Laboratory with wave/tow tank, engineering tank and water/wind tunnels, the Tidal Energy Test Site at General Sullivan Bridge, the UNH Pier and the AMAC/wave and offshore wind energy test site. The FERC-permitted Tidal Energy Test Site has currents of greater than 4 knots (max. 5 knots) and is a large-scale test site that can accommodate turbines up to 4 meter (13 ft) in diameter. The research-permitted offshore test site is located in state waters at the UNH Atlantic Marine Aquaculture (AMAC) site in 170 ft (52 m) of water approximately 6 miles from the New Hampshire coast, and is a full-scale wave energy test site and a scaled offshore wind energy test site. A mooring grid was successfully deployed under extreme New England winter conditions for the past 10+ years. Existing and newly developed infrastructure, including support vessels, and the off-the shelf availability of environmental and survey data enable very cost-effective open water test sites.
Howard Stone, Professor of Mechanical and Aerospace Engineering at Princeton University will be giving a lecture entitled: “Title: Bacteria, Biofilms and Fluid Dynamics: Elementary Flows and Unexpected Phenomena” as part of the Albert Kobayashi and Jim Morrison Lecture Series.
Bacterial biofilms have an enormous impact on medicine, industry and ecology. These microbial communities are generally considered to adhere to surfaces or interfaces. In most practical situations, the biofilms are exposed to flow. We investigate two features of such systems: (i) We examine the migration of bacteria along surfaces when exposed to a shear flow. In particular, we identify an unusual response where flow produces a directed motion of twitching bacteria in the upstream direction. (ii) We report the formation of biofilm streamers (threads of biofilm) suspended in the middle plane of curved micro channels under conditions of laminar flow. We use numerical simulations of the three-dimensional flow in curved channels to highlight the presence of a secondary vortical motion in the proximity of the corners, which suggests an underlying hydrodynamic mechanism responsible for the formation of the streamers. Thus, we bring together experiments, simulations, and models for the fluid-structure interaction to rationalize the spatial and temporal development of bacterial streamers.
On May 13-18th, a 5 day workshop was held at the Banff International Research Station with the topic “Connections Between Regularized and Large-Eddy Simulation Methods for Turbulence.” Videos of the talks given at the workshop can be found here.
Superhydrophobic Surfaces Friction Reduction under Partial and Complete Wetting
Surface microtexturing can lead to a superhydrophobic Cassie-Baxter state characterized by the presence of air pockets within the roughness. It is widely believed that these air pockets act as effective “shear free” (or at least shear reducing) regions that lead to lower global friction. In this talk we will explore the effects of pressure on the degree of microtexturing wetting and corresponding friction reduction characteristics in microchannel flow. It will be shown that friction reduction is for the most part insensitive to the degree of microtexturing wetting. Furthermore, under certain conditions a fully wetted Wenzel state can lead to lower friction characteristics than those of the un-wetted Cassie-Baxter state. Hydrodynamics and physicochemical interfacial phenomena provide insight into these behaviors. These findings can have major implications in the way we think about how these surfaces achieve friction reduction and in the optimization of microgeometries for specific applications.
Dr. Carlos Hidrovo is an assistant professor of mechanical engineering at The University of Texas at Austin. He earned his Ph.D. in mechanical engineering from MIT in 2001. Dr. Hidrovo worked as a Research Scientist in the 3D Optical Systems group at MIT and as a Research Associate in the Micro Heat Transfer Laboratory at Stanford University before joining the faculty of UT Austin in September 2007. He is the recipient of a 2012 NSF CAREER Award from the Fluid Dynamics program, the 2008 DARPA Young Faculty Award, and the ASME 2001 Robert T. Knapp Award. Dr. Hidrovo research interests lie at the intersection of multiscale and multiphase flow and transport phenomena, surface tension interactions in micro/nanoengineered structures, and electrokinetic ion transport in porous media for applications in energy storage, portable biochemical diagnostics, thermal management, and water treatment systems. He is also actively involved in developing novel imaging and diagnostic tools in these areas.