137 research outputs found
Design Optimization of a Boundary Layer Ingestion Propulsion System for a Long-Range, High-Altitude UAV
Recent studies have proposed using Boundary Layer Ingestion propulsion systems utilizing turboelectric generators to increase fuel efficiency in the next generation of airliners. Another aircraft platform where fuel savings would be highly valuable would be long-range UAVs. Therefore, a design optimization study was conducted on a BLI propulsor for an adaptation of a RQ-4 Global Hawk airframe, which is an airframe that is already proven to be ideal for long range missions. The study was performed on STAR CCM+ CFD software, using the Design Manager feature within the program. The interest was in optimizing the propulsor for cruise conditions, when the fuel savings will be most valuable in achieving a longer range. An initial simulation was performed, to act as the reference simulation for the Design Manager study. After initial values were obtained, the Design Manager study was conducted in two different iterations, searching for the ideal design. A variety of geometric variables were input into the Design Manager, such as inlet and outlet cross-sectional area, and the shape of the inner engine. Upon completion of the study, an ideal design of a BLI propulsor was found. The total power necessary to achieve static equilibrium flight was reduced from 222 MW to 193.2 MW, a savings of 12.87%. Such power savings are significant considering that a BLI propulsor already achieves fuel savings compared with a traditional propulsor that ingests air traveling at the free stream velocity. This study acts as a rationale for the further development of a physical scale model to validate such results, and the possibility of commercial development if satisfactory results are obtained
Bicycle Wheel Aerodynamics Predictions Using CFD: Efficiency Using Blade Element Theory
The cycling industry has long relied on expensive wind tunnel testing when designing aerodynamic products, particularly in the context of wheels which account for 10 to 15 percent of a cyclist’s total aerodynamic drag. With the recent advent of computational fluid dynamics, the industry now has an economical tool to supplement the wheel design process; however, the complex nature of rotating spoked wheels requires high resolution meshes to model at acceptable fidelity. This research investigates an alternative CFD method that lowers the computational cost of modeling aerodynamic bicycle wheels by modeling spokes using blade element momentum virtual disks. Two CFD models of a HED Trispoke wheel, one with resolved spokes (physical mesh) and one with modeled spokes (virtual disk), are compared to existing CFD and wind tunnel drag coefficient data at various headwind speeds and angles. Preliminary data shows good agreement
Spiking Optical Patterns and Synchronization
We analyze the time resolved spike statistics of a solitary and two mutually
interacting chaotic semiconductor lasers whose chaos is characterized by
apparently random, short intensity spikes. Repulsion between two successive
spikes is observed, resulting in a refractory period which is largest at laser
threshold. For time intervals between spikes greater than the refractory
period, the distribution of the intervals follows a Poisson distribution. The
spiking pattern is highly periodic over time windows corresponding to the
optical length of the external cavity, with a slow change of the spiking
pattern as time increases. When zero-lag synchronization between the two lasers
is established, the statistics of the nearly perfectly matched spikes are not
altered. The similarity of these features to those found in complex interacting
neural networks, suggests the use of laser systems as simpler physical models
for neural networks
Stable isochronal synchronization of mutually coupled chaotic lasers
The dynamics of two mutually coupled chaotic diode lasers are investigated
experimentally and numerically. By adding self feedback to each laser, stable
isochronal synchronization is established. This stability, which can be
achieved for symmetric operation, is essential for constructing an optical
public-channel cryptographic system. The experimental results on diode lasers
are well described by rate equations of coupled single mode lasers
Flat (001) surfaces of II-VI semiconductors: A lattice gas model
We present a two-dimensional lattice gas with anisotropic interactions which
model the known properties of the surface reconstructions of CdTe and ZnSe. In
constrast to an earlier publication [12], the formation of anion dimers is
considered. This alters the behaviour of the model considerably. We determine
the phase diagram of this model by means of transfer matrix calculations and
Monte Carlo simulations. We find qualitative agreement with the results of
various experimental investigations.Comment: 17 pages, 5 figures. See http://theorie.physik.uni-wuerzburg.de/~ahr/
for related publication
Unravelling quantum carpets: a travelling wave approach
Quantum carpets are generic spacetime patterns formed in the probability
distributions P(x,t) of one-dimensional quantum particles, first discovered in
1995. For the case of an infinite square well potential, these patterns are
shown to have a detailed quantitative explanation in terms of a travelling-wave
decomposition of P(x,t). Each wave directly yields the time-averaged structure
of P(x,t) along the (quantised)spacetime direction in which the wave
propagates. The decomposition leads to new predictions of locations, widths
depths and shapes of carpet structures, and results are also applicable to
light diffracted by a periodic grating and to the quantum rotator. A simple
connection between the waves and the Wigner function of the initial state of
the particle is demonstrated, and some results for more general potentials are
given.Comment: Latex, 26 pages + 6 figures, submitted to J. Phys. A (connections
with prior literature clarified
Вплив нормального тиску на напружений стан гуми ступінчастого каната на робочому органі підйомної машини
Досліджено напружений стан гуми ступінчастого гумотросового каната у разі його застосування на підйомній машині з бобінним робочим органом та зі шківом тертя. Показано, що максимальні напруження в гумі залежать від конструкції каната та тиску, що виникає поміж шарами. Форма поперечного перерізу троса також впливає на напружений стан гуми.Исследовано напряженное состояние резины ступенчатого резинотросового каната в случае его применения на подъемной машине с бобинным рабочим органом и со шкивом трения. Показано, что максимальные напряжения в резине зависят от конструкции каната и давления, возникающего между слоями. Форма поперечного сечения троса также влияет на напряженное состояние резины.The stress-strain state of stepped rubber-rope cable in bobbin of winding and in pulley friction, are investigated. Shown that the maximum stress in the rubber depends on the design of the rope and the pressure appeared between the layers. Cable cross-sectional shape also affects to the stressstrain state of rubber
Public-channel cryptography based on mutual chaos pass filters
We study the mutual coupling of chaotic lasers and observe both
experimentally and in numeric simulations, that there exists a regime of
parameters for which two mutually coupled chaotic lasers establish isochronal
synchronization, while a third laser coupled unidirectionally to one of the
pair, does not synchronize. We then propose a cryptographic scheme, based on
the advantage of mutual-coupling over unidirectional coupling, where all the
parameters of the system are public knowledge. We numerically demonstrate that
in such a scheme the two communicating lasers can add a message signal
(compressed binary message) to the transmitted coupling signal, and recover the
message in both directions with high fidelity by using a mutual chaos pass
filter procedure. An attacker however, fails to recover an errorless message
even if he amplifies the coupling signal
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