552 research outputs found
CFD Analysis of Helicopter Wakes in Ground Effect
The paper presents CFD results for the wake of a helicopter flying a low altitude at different advance ratios.
The wakes are assessed in terms of topology and velocity magnitudes. The structure of the wake near ground
changes rapidly with the advance ratio and its decay appears to be faster than what is suggested by theoretical
analyses. The results show clear the potential of modern CFD for use in helicopter safety and highlights the
need for detailed surveys of helicopter wakes using full-scale physical experiments
Multi-Modal Human-Machine Communication for Instructing Robot Grasping Tasks
A major challenge for the realization of intelligent robots is to supply them
with cognitive abilities in order to allow ordinary users to program them
easily and intuitively. One way of such programming is teaching work tasks by
interactive demonstration. To make this effective and convenient for the user,
the machine must be capable to establish a common focus of attention and be
able to use and integrate spoken instructions, visual perceptions, and
non-verbal clues like gestural commands. We report progress in building a
hybrid architecture that combines statistical methods, neural networks, and
finite state machines into an integrated system for instructing grasping tasks
by man-machine interaction. The system combines the GRAVIS-robot for visual
attention and gestural instruction with an intelligent interface for speech
recognition and linguistic interpretation, and an modality fusion module to
allow multi-modal task-oriented man-machine communication with respect to
dextrous robot manipulation of objects.Comment: 7 pages, 8 figure
CFD Analysis of Helicopter Wakes in Ground Effect
The paper presents CFD results for the wake of a helicopter flying a low altitude at different advance ratios.
The wakes are assessed in terms of topology and velocity magnitudes. The structure of the wake near ground
changes rapidly with the advance ratio and its decay appears to be faster than what is suggested by theoretical
analyses. The results show clear the potential of modern CFD for use in helicopter safety and highlights the
need for detailed surveys of helicopter wakes using full-scale physical experiments
Nitrogen compounds and ozone in the stratosphere: comparison of MIPAS satellite data with the Chemistry Climate Model ECHAM5/MESSy1
International audienceThe chemistry climate model ECHAM5/MESSy1 (E5/M1) in a setup extending from the surface to 80 km with a vertical resolution of about 600 m near the tropopause with nudged tropospheric meteorology allows a direct comparison with satellite data of chemical species at the same time and location. Here we present results out of a transient 10 years simulation for the period of the Antarctic vortex split in September 2002, where data of MIPAS on the ENVISAT-satellite are available. For the first time this satellite instrument opens the opportunity, to evaluate all stratospheric nitrogen containing species simultaneously with a good global coverage, including the source gas N2O which allows an estimate for NOx-production in the stratosphere. We show correlations between simulated and observed species in the altitude region between 10 and 50 hpa for different latitude belts, together with the Probability Density Functions (PDFs) of model results and observations. This is supplemented by global charts on pressure levels showing the satellite data and the simulated data sampled at the same time and location. We demonstrate that the model in most cases captures the partitioning in the nitrogen family, the diurnal cycles and the spatial distribution within experimental uncertainty. There appears to be, however, a problem to reproduce the observed nighttime partitioning between N2O5 and NO2 in the middle stratosphere
Ultrafast element-resolved magneto-optics using a fiber-laser-driven extreme ultraviolet light source
We present a novel setup to measure the transverse magneto-optical Kerr
effect in the extreme ultraviolet spectral range at exceptionally high
repetition rates based on a fiber laser amplifier system. This affords a very
high and stable flux of extreme ultraviolet light, which we use to measure
element-resolved demagnetization dynamics with unprecedented depth of
information. Furthermore, the setup is equipped with a strong electromagnet and
a cryostat, allowing measurements between 10 and 420 K using magnetic fields up
to 0.86 T. The performance of our setup is demonstrated by a set of
temperature- and time-dependent magnetization measurements showing distinct
element-dependent behavior
A fast stratospheric chemistry solver: the E4CHEM submodel for the atmospheric chemistry global circulation model EMAC
The atmospheric chemistry general circulation model ECHAM5/MESSy (EMAC) and the atmospheric chemistry box model CAABA are extended by a computationally very efficient submodel for atmospheric chemistry, E4CHEM. It focuses on stratospheric chemistry but also includes background tropospheric chemistry. It is based on the chemistry of MAECHAM4-CHEM and is intended to serve as a simple and fast alternative to the flexible but also computationally more demanding submodel MECCA. In a model setup with E4CHEM, EMAC is now also suitable for simulations of longer time scales. The reaction mechanism contains basic O3, CH4, CO, HOx, NOx, and ClOx gas phase chemistry. In addition, E4CHEM includes optional fast routines for heterogeneous reactions on sulphate aerosols and polar stratospheric clouds (substituting the existing submodels PSC and HETCHEM), and scavenging (substituting the existing submodel SCAV). We describe the implementation of E4CHEM into the MESSy structure of CAABA and EMAC. For some species the steady state in the box model differs by up to 100% when compared to results from CAABA/MECCA due to different reaction rates. After an update of the reaction rates in E4CHEM the mixing ratios in both boxmodel and 3-D model simulations are in satisfactory agreement with the results from a simulation where MECCA with a similar chemistry scheme was employed. Finally, a comparison against a simulation with a more complex and already evaluated chemical mechanism is presented in order to discuss shortcomings associated with the simplification of the chemical mechanism
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