A Few Past Projects
Principal Investigator Marc Ramsey
Energetic Cavitation Collapse
At Vanderbilt, Dr. Ramsey developed a tabletop device that can drive the symmetric collapse of a 4 mm vapor bubble in water at 22 bar. Nanosecond stroboscopic photography and single-shot streak imaging reveals a stagnation plasma of 28 micron radius at over 12,000 K and an unprecedented pressure of 3.2 Mbar. Compared to Single Bubble Sonoluminescence (SBSL), the most commonly studied cavitation mechanism, this event is greater by factors of 30 in size, 1,000,000 in energy, and 100 in stagnation pressure. This facility is now available at RAPA for study of dense plasmas and equations of state of liquids at megabar pressures.
As part of his cavitation work, Dr. Ramsey developed a custom simulation of the event solving the full compressible Navier-Stokes equations for both the liquid and the bubble interior using realistic equations of state. Theses plots show spatial profiles of the liquid properties at discrete times corresponding to (a) ‑35, (b) ‑16, (c) ‑6.4, (d) ‑1.3, (e) 0.0, and (f) 6.5 nanoseconds from the moment of minimum radius. Short-dash (red) line is the value at the bubble wall, and long-dash (blue) line is the shock envelope.
Instant Air Meter for Fresh Concrete
At Creare, Dr. Ramsey developed a novel acoustic technique for measuring the volume fraction and size of entrained air bubbles in fresh concrete. A system of air voids in cured concrete provides resistance to water expansion damage during freeze-thaw cycles. It is important to monitor the critical entrained air parameters in fresh concrete as it is produced and delivered to the jobsite. Existing measurement methods are cumbersome, prone to error, and measure only void fraction, giving no information about specific surface or spacing factor. The Creare Instant Air Meter provides an instantaneous, in-situ measurement of both void fraction and specific surface. This simple, robust, handheld wand can be inserted into any fresh concrete sample and returns an accurate result at the touch of a button, enabling real-time monitoring at the jobsite.
Bladder Volume Sensor
At Creare, Dr. Ramsey developed a novel acoustic technology for measuring liquid volume in flexible bladders known as Volume by Acoustic Reverberation Decay (VARD). The Advanced Space Suit carries consumable cooling water maintained at ambient pressure within a bladder, and no known sensor is suitable for monitoring its volume. We developed a simple, low power sensor that accurately measures the volume of fluid in any soft-walled bladder. The innovative sensing technique provides an accurate measurement that is insensitive to gravity, the motion and geometry of the reservoir, the presence of air, and electromagnetic interference.
While at Creare, Dr. Ramsey upgraded the Air Force RamGun, a test facility used to expose candidate structural joints to hydrodynamic ram, simulating the effect of artillery impact on an aircraft fuel bay. A projectile launched by a gas gun impacts a water filled chamber to create a pressure wave that impinges on a test article. We dramaticaly improved the operating range, repeatability, and utility of the RamGun facility by fitting it with acoustically optimized hardware that produces a clean, repeatable, planar pressure wave, making test results more controlled and meaningful. In addition, by efficiently converting all of the projectile’s kinetic energy into hydrodynamic pressure, it produces a higher amplitude pressure wave without facility damage.
Molecular Tagging Velocimetry
Dr. Ramsey developed new experimental and data reduction techniques for molecular tagging velocimetry, a laser diagnostic approach in which molecules within a flow are tagged, fluoresced, and imaged at different times. He used these methods to measure the velocity field in the exhaust of an over-expanded rocket nozzle. These measurements settled a long-standing question regarding the existence of a recirculation region in downstream of the Mach stem predicted by numerical simulation, definitively demonstrating that it does not occur. He also contributed to measurements in the wake of a strut in a scramjet combustor and the bow shock of a hypervelocity projectile in a shock tunnel.
At Sandia National Laboratories, Dr. Ramsey helped develop a series of single-element deformable mirrors for thermal lens compensation in rod and slab laser amplifiers. The novel devices employed carefully tuned geometry and a single actuator to produce variable focus by deforming a planar mirror in on-axis, off-axis, and cylindrical configurations.