55,138 research outputs found
Droplet size and morphology characterization for diesel sprays under atmospheric operating conditions
The shape of microscopic fuel droplets may differ from the perfect sphere, affecting their external surface area and thus the heat transfer with the surrounding gas. Hence there is a need for the characterization of droplet shapes, and the estimation of external surface area, in order to enable the development of physically accurate mathematical models for the heating and evaporation of diesel fuel sprays. We present ongoing work to automat-ically identify and reconstruct the morphology of fuel droplets, primarily focusing in this study on irregularly-shaped, partially-deformed and oscillating droplets under atmospheric conditions. We used direct imaging tech-niques based on long-working distance microscopy and ultra-high-speed video to conduct a detailed temporal investigation of droplet morphology. We applied purpose-built algorithms to extract droplet size, velocity, vol-ume and external surface area from the microscopic ultra-high-speed video frames. High resolution images of oscillating droplets and a formation of a droplet form ligament, sphericity factors, volume as well as external surface area are presented for 500 bar injection pressure in the near nozzle region (up to 0.7 mm from nozzle exit) under atmospheric conditions. We observed a range of different liquid structures, including perfectly spher-ical, non-spherical droplets and stretched ligaments. We found that large droplets and ligaments exceeding the size of the nozzle hole could be found at the end of injection. In order to estimate droplet volume and external surface area from two-dimensional droplet information, a discrete revolution of the droplet silhouette about its major centroidal axis was used. Special attention was paid to the estimation of actual errors in the prediction of volume and surface characteristics from a droplet silhouette. In addition to the estimation of droplet volume and external surface area, the actual shape reconstruction in 3D coordinates from a droplet silhouette was performed in order to enable future numerical modelling studies of real droplets
LSST optical beam simulator
We describe a camera beam simulator for the LSST which is capable of
illuminating a 60mm field at f/1.2 with realistic astronomical scenes, enabling
studies of CCD astrometric and photometric performance. The goal is to fully
simulate LSST observing, in order to characterize charge transport and other
features in the thick fully depleted CCDs and to probe low level systematics
under realistic conditions. The automated system simulates the centrally
obscured LSST beam and sky scenes, including the spectral shape of the night
sky. The doubly telecentric design uses a nearly unit magnification design
consisting of a spherical mirror, three BK7 lenses, and one beam-splitter
window. To achieve the relatively large field the beam-splitter window is used
twice. The motivation for this LSST beam test facility was driven by the need
to fully characterize a new generation of thick fully-depleted CCDs, and assess
their suitability for the broad range of science which is planned for LSST. Due
to the fast beam illumination and the thick silicon design [each pixel is 10
microns wide and over 100 microns deep] at long wavelengths there can be
effects of photon transport and charge transport in the high purity silicon.
The focal surface covers a field more than sufficient for a 40x40 mm LSST CCD.
Delivered optical quality meets design goals, with 50% energy within a 5 micron
circle. The tests of CCD performance are briefly described.Comment: 9 pages, 9 figure
State Estimation for Kite Power Systems with Delayed Sensor Measurements
We present a novel estimation approach for airborne wind energy systems with ground-based control and energy generation. The estimator fuses measurements from an inertial measurement unit attached to a tethered wing and position measurements from a camera as well as line angle sensors in an unscented Kalman filter. We have developed a novel kinematic description for tethered wings to specifically address tether dynamics. The presented approach simultaneously estimates feedback variables for a flight controller as well as model parameters, such as a time-varying delay. We demonstrate the performance of the estimator for experimental flight data and compare it to a state-of-the-art estimator based on inertial measurements
The Quest for the Most Spherical Bubble
We describe a recently realized experiment producing the most spherical
cavitation bubbles today. The bubbles grow inside a liquid from a point-plasma
generated by a nanosecond laser pulse. Unlike in previous studies, the laser is
focussed by a parabolic mirror, resulting in a plasma of unprecedented
symmetry. The ensuing bubbles are sufficiently spherical that the hydrostatic
pressure gradient caused by gravity becomes the dominant source of asymmetry in
the collapse and rebound of the cavitation bubbles. To avoid this natural
source of asymmetry, the whole experiment is therefore performed in
microgravity conditions (ESA, 53rd and 56th parabolic flight campaign).
Cavitation bubbles were observed in microgravity (~0g), where their collapse
and rebound remain spherical, and in normal gravity (1g) to hyper-gravity
(1.8g), where a gravity-driven jet appears. Here, we describe the experimental
setup and technical results, and overview the science data. A selection of
high-quality shadowgraphy movies and time-resolved pressure data is published
online.Comment: 18 pages, 14 figures, 1 tabl
3D Camouflaging Object using RGB-D Sensors
This paper proposes a new optical camouflage system that uses RGB-D cameras,
for acquiring point cloud of background scene, and tracking observers eyes.
This system enables a user to conceal an object located behind a display that
surrounded by 3D objects. If we considered here the tracked point of observer s
eyes is a light source, the system will work on estimating shadow shape of the
display device that falls on the objects in background. The system uses the 3d
observer s eyes and the locations of display corners to predict their shadow
points which have nearest neighbors in the constructed point cloud of
background scene.Comment: 6 pages, 12 figures, 2017 IEEE International Conference on SM
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