Edward F. Romero

Diagnostics for liquid dispersion due to a high-speed impact with accident or vulnerability assessment application

The high-speed impact and subsequent dispersion of a large liquid slug is of interest for assessing vulnerability of structures when subjected to such an event. The Weber number associated with such liquid impacts is generally between 105 and 108. Because of the experiment scale and destructive nature of these high-energy impacts, most traditional diagnostics are difficult to implement. Therefore, unique diagnostics were employed in several tests to gather information on impact force, spreading instability, slug break-up, ejection velocity, droplet deformation and spray characteristics. Measurement techniques discussed here include high-speed photometrics, particle image velocimetry (PIV), TrackEye particle analysis, speckle correlation, single-pass schlieren imaging, phase Doppler particle analyzer (PDPA) and load cell measurements as applied to large-scale, high-speed liquid impacts.

Vibrafuge: Re-Entry and Launch Test Simulation in a Combined Linear Acceleration and Vibration Environment

Sandia National Laboratories has developed a new technique for testing in a combined linear acceleration and vibration environment. Amplified piezo-electric actuator assemblies are used in combination with Sandia’s 29-ft centrifuge facility to surpass the load capabilities of previous attempts using traditional mechanical shaker systems. The piezoelectric actuators are lightweight, modular and overcome several limitations presented by a mechanical shaker. They are ‘scalable’, that is, adding more piezo-electric units in parallel or in series can support larger-weight test articles or wider range of displacement/frequency regimes. In addition, the units could be mounted on the centrifuge arm in various configurations to provide a variety of input directions. The design along with test results will be presented to demonstrate the capabilities of the new piezo-electric Vibrafuge.

Application of stereo laser tracking methods for quantifying flight dynamics-II

Conventional tracking systems measure time-space-position data and collect imagery to quantify the flight dynamics of tracked targets. One of the major obstacles that severely impacts the accuracy and fidelity of the target characterization is atmospheric turbulence induced distortions of the tracking laser beam at the target surface and imagery degradations. Tracking occurs in a continuously changing atmosphere resulting in rapid variations in the tracking laser beam and distorted imagery. These atmospheric effects, in combination with other sources of degradation, such as measurement system motions (e.g. vibration/jitter), defocus blur, and spatially varying noise, severely limit the useful and accuracy of many tracking and analysis methods. This paper discusses the viability of employing stereo image correlation methods for high speed moving target characterization through atmospheric turbulence. Stereo imaging methods have proven effective in the laboratory for quantifying temporally and spatially resolved 3D motions across a target surface. This technique acquires stereo views (two or more) of a test article that has an applied random speckled (dot) pattern painted on the surface to provide trackable features on the entire target surface. The stereo views are reconciled via coordinate transformations and correlation of the transformed images. The principle limitations of this method have been the need for clean imagery and fixed camera positions and orientations. However, recent field tests have demonstrated that these limitations can be overcome to provide a new method for quantifying flight dynamics with stereo laser tracking and multi-video imagery in the presence of atmospheric turbulence.

High force vibration testing with wide frequency range

A shaker assembly for vibration testing includes first and second shakers, where the first shaker includes a piezo-electric material for generating vibration. A support structure permits a test object to be supported for vibration of the test object by both shakers. An input permits an external vibration controller to control vibration of the shakers.

Laser tracker TSPI uncertainty quantification via centrifuge trajectory

Sandia National Laboratories currently utilizes two laser tracking systems to provide time-space-position-information (TSPI) and high speed digital imaging of test units under flight. These laser trackers have been in operation for decades under the premise of theoretical accuracies based on system design and operator estimates. Advances in optical imaging and atmospheric tracking technology have enabled opportunities to provide more precise six degree of freedom measurements from these trackers. Applying these technologies to the laser trackers requires quantified understanding of their current errors and uncertainty. It was well understood that an assortment of variables contributed to laser tracker uncertainty but the magnitude of these contributions was not quantified and documented. A series of experiments was performed at Sandia National Laboratories large centrifuge complex to quantify TSPI uncertainties of Sandia National Laboratories laser tracker III. The centrifuge was used to provide repeatable and economical test unit trajectories of a test-unit to use for TSPI comparison and uncertainty analysis. On a centrifuge, testunits undergo a known trajectory continuously with a known angular velocity. Each revolution may represent an independent test, which may be repeated many times over for magnitudes of data practical for statistical analysis. Previously these tests were performed at Sandias rocket sled track facility but were found to be costly with challenges in the measurement ground truth TSPI. The centrifuge along with on-board measurement equipment was used to provide known ground truth position of test units. This paper discusses the experimental design and techniques used to arrive at measures of laser tracker error and uncertainty.