Fine structure of Vavilov-Cherenkov radiation near the Cherenkov threshold

We analyze the Vavilov-Cherenkov radiation (VCR) in a dispersive nontransparent dielectric air-like medium both below and above the Cherenkov threshold, in the framework of classical electrodynamics. It is shown that the transition to the subthreshold energies leads to the destruction of electromagnetic shock waves and to the sharp reduction of the frequency domain where VCR is emitted. The fine wake-like structure of the Vavilov-Cherenkov radiation survives and manifests the existence of the subthreshold radiation in the domain of anomalous dispersion. These domains can approximately be defined by the two phenomenological parameters of the medium, namely, the effective frequency of oscillators and the damping describing an interaction with the other degrees of freedom.Comment: 9 pages, 6 figure

Effects of fish-meal, cow blood-meal, and sorghum diets on food utilization and growth of cage cultured Sarotherodon niloticus

The growth responses and feed utilization of Sarotherodon niloticus held in metal cages in a pond and fed diets containing fish-meal, cow blood-meal or sorghum was studied. Results indicate that the best growth, feed conversion and protein efficiency ratio were obtained with the diet containing 60% fish-meal. The growth performance of fish on 40% fish-meal, and 40% and 60% blood meal were not significantly different, and were quite close to the performance with 60% fish-meal. The growth and food utilization of fish on 84% sorghum diet was significantly lower than the rest. The Caged fish without supplemental feeding had a light gain in weight. All fish with supplemental feeding appeared healthy. It is concluded that cow blood meal at 40% or 60% inclusion in diet can adequately replace fish-meal in S. niloticus supplemental diet in pond cultur

Variable-speed tail rotors for helicopters with variable-speed main rotors

Variable tail rotor speed is investigated as a method for reducing tail rotor power, and improving helicopter performance. A helicopter model able to predict the main rotor and tail rotor powers is presented, and the flight test data of the UH-60A helicopter is used for validation. The predictions of the main and tail rotor powers are generally in good agreement with flight tests, which justifies the use of the present method in analyzing main and tail rotors. Reducing the main rotor speed can result in lower main rotor power at certain flight conditions. However, it increases the main rotor torque and the corresponding required tail rotor thrust to trim, which then decreases the yaw control margin of the tail rotor. In hover, the tail rotor may not be able to provide enough thrust to counter the main rotor torque, if it is slowed to follow the main rotor speed. The main rotor speed corresponding to the minimum main rotor power increases, if the change of tail rotor power in hover is considered. As a helicopter translated to cruise, the induced power decreases, and the profile power increases, with the profile power dominating the tail rotor. Reducing the tail rotor speed in cruise reduces the profile power to give a 37% reduction in total tail rotor power and a 1.4% reduction to total helicopter power. In high speed flight, varying the tail rotor speed is ineffective for power reduction. The power reduction obtained by the variable tail rotor speed is reduced for increased helicopter weight

Effects of feedback, mobility and index of difficulty on deictic spatial audio target acquisition in the horizontal plane

We present the results of an empirical study investigating the effect of feedback, mobility and index of difficulty on a deictic spatial audio target acquisition task in the horizontal plane in front of a user. With audio feedback, spatial audio display elements are found to enable usable deictic interac-tion that can be described using Fitts law. Feedback does not affect perceived workload or preferred walking speed compared to interaction without feedback. Mobility is found to degrade interaction speed and accuracy by 20%. Participants were able to perform deictic spatial audio target acquisition when mobile while walking at 73% of their pre-ferred walking speed. The proposed feedback design is ex-amined in detail and the effects of variable target widths are quantified. Deictic interaction with a spatial audio display is found to be a feasible solution for future interface designs

Modelling the rapid spherical compression of isotropic turbulence

Rapid distortion analysis is used to modify the form of the closure model for the dissipation rate of the turbulent kinetic energy. The modification is such that the evolution of the dissipation rate during a rapid compression is predicted exactly; good agreement between the model prediction and direct simulation data is obtained. Previous closure proposals fail to properly predict the rapid compression case. The reason for the difference between the present and previous models is traced to the fact that previous workers neglected variations of kinematic viscosit

Parallel Evaluation of Quantum Algorithms for Computational Fluid Dynamics

The development and evaluation of quantum computing algorithms for computational fluid dynamics is described along with a detailed analysis of the parallel performance of a quantum computer simulator developed as part of the present work. The quantum computer simulator is used in the evaluation of the quantum algorithms on a conventional parallel computer, and is applied to quantum lattice-based algorithms as well as the Poisson equation. A key result is a demonstration of how the Poisson equation can be solved effeciently on a quantum computer, while its use within a larger algorithm representing a full CFD solver poses a number of signifi- cant challenges

Prediction of Helicopter Rotor Hover Performance using High Fidelity CFD Methods

No abstract available

Asymptotic Solutions of the Phase Space Schrodinger Equation: Anisotropic Gaussian Approximation

We consider the singular semiclassical initial value problem for the phase space Schrodinger equation. We approximate semiclassical quantum evolution in phase space by analyzing initial states as superpositions of Gaussian wave packets and applying individually semiclassical anisotropic Gaussian wave packet dynamics, which is based on the the nearby orbit approximation; we accordingly construct a semiclassical approximation of the phase space propagator, semiclassical wave packet propagator, which admits WKBM semiclassical states as initial data. By the semiclassical propagator we construct asymptotic solutions of the phase space Schrodinger equation, noting the connection of this construction to the initial value repsresentations for the Schrodinger equation

Numerical Simulations on the PSP Rotor Using HMB3

This work presents CFD analyses of the isolated Pressure Sensitive Paint (PSP) model rotor blade in hover and forward flight using the structured multi-block CFD solver of Glasgow University. In hover, two blade-tip Mach numbers (0.585 and 0.65) were simulated for a range of blade pitch angles using fully-turbulent flow and the k-ω SST model. Results at blade-tip Mach number of 0.585 showed a fair agreement with experimental Figure of Merit and surface pressure coefficients obtained in the Rotor Test Cell (RTC) at NASA Langley Research Center. Comparisons are presented at blade-tip Mach number of 0.65 in terms of integral blade loads, surface pressure coefficients and position of the tip-vortex cores with published numerical data. Finally, the flow around the PSP rotor in forward flight was also computed at medium thrust (CT =0.006) and results were compared with published experimental data

Coupled flight dynamics and CFD - demonstration for helicopters in shipborne environment

The development of high-performance computing and computational fluid dynamics methods have evolved to the point where it is possible to simulate complete helicopter configurations with good accuracy. Computational fluid dynamics methods have also been applied to problems such as rotor/fuselage and main/tail rotor interactions, performance studies in hover and forward flight, rotor design, and so on. The GOAHEAD project is a good example of a coordinated effort to validate computational fluid dynamics for complex helicopter configurations. Nevertheless, current efforts are limited to steady flight and focus mainly on expanding the edges of the flight envelope. The present work tackles the problem of simulating manoeuvring flight in a computational fluid dynamics environment by integrating a moving grid method and the helicopter flight mechanics solver with computational fluid dynamics. After a discussion of previous works carried out on the subject and a description of the methods used, validation of the computational fluid dynamics for ship airwake flow and rotorcraft flight at low advance ratio are presented. Finally, the results obtained for manoeuvring flight cases are presented and discussed