The Use of Inverse Simulation for Conceptual Design

No abstract available

Development and verification of an algorithm for helicopter inverse simulation

No abstract available

Modelling and Classification of Helicopter Combat Manoeuvres

No abstract available

Mathematical Definition of Helicopter Manoeuvres. Internal report no. 9225

There is an increasing number of flight mechanics studies where the influence of manoeuvre type has been found to be of importance. A notable example has been the upgrade to the U.S. Mil. Spec, for handling qualities which includes a set of aggressive tasks to be flown as part of the flight test requirements. Another recent development has been the wider use of inverse simulation where a flight path is used to drive a helicopter mathematical model, the aim being to calculate the control actions corresponding to the flight path being flown. Although the evaluation of helicopter performance through the use of standard manoeuvres has become established, there is little information available on the precise form of the manoeuvre, or on how mathematical representations may be constructed. The aim of this paper has been to categorise the various types of manoeuvre commonly used in helicopter military operations, and then to develop algorithms capable of defining them mathematically. Several manoeuvres are fully modelled in the paper, and it becomes apparent that the techniques used may be applied to a variety of different manoeuvres. By way of validation, data from flight tests has been used for comparisons with modelled flight paths and manoeuvre parameters. Methods of grading manoeuvres are also presented along with a discussion on the choice of suitable mathematical functions

The Simulation of Recovery Procedures from Engine Failures during Helicopter Offshore Operations. Internal report no. 9331

This report discusses the mathematical models and the specialised simulation techniques developed for an investigation of helicopter offshore operations under adverse conditions. The development of a mathematical model of a torque limited, twin engine power plant capable of accommodating multiple or single gas turbine failures is presented. In order to simulate engine failures during the critical phases of takeoff or landing manoeuvres, a novel hybrid simulation technique called HIFIS which incorporates both inverse and forward methods has been developed. Its formulation and the subsequent specialised recovery trajectories that it requires are detailed

Helicopter Takeoff and Landing Procedures in Adverse Conditions using Inverse Simulation. Progress note: Oct. 92 - Sept. 93. Internal report no. 9332

This report summarises the progress made in the second year of a study of helicopter offshore operations in adverse conditions. Initially, a narrative description of key helicopter heli-deck related manoeuvres in the presence and absence of engine failures, is given. Based on this information, mathematical models of the manoeuvres are developed in a form suitable for use as input to inverse simulation. The demands of simulating pilot strategies in the event of engine failures has necessitated the development of a multistage inverse-forward-inverse simulation technique of novel kind and a comprehensive description of this method is presented. A dynamic graphics package has been created to demonstrate piloting strategies and its formulation is briefly outlined. The piloting strategies as derived from simulation studies are presented for the Towering Takeoff and Normal Approach and Landing manoeuvres (with and without engine failures) and these are qualitatively validated against descriptions provided by practicing pilots. Finally, some conclusions are drawn and directions for future work highlighted

Loading a vapor cell magneto-optic trap using light-induced atom desorption

Low intensity white light was used to increase the loading rate of $^{87}$Rb atoms into a vapor cell magneto-optic trap by inducing non-thermal desorption of Rb atoms from the stainless steel walls of the vapor cell. An increased Rb partial pressure reached a new equilibrium value in less than 10 seconds after switching on the broadband light source. After the source was turned off, the partial pressure returned to its previous value in $1/e$ times as short as 10 seconds.Comment: 7 pages, 6 figure

Effect of anharmonicities in the critical number of trapped condensed atoms with attractive two-body interaction

We determine the quantitative effect, in the maximum number of particles and other static observables, due to small anharmonic terms added to the confining potential of an atomic condensed system with negative two-body interaction. As an example of how a cubic or quartic anharmonic term can affect the maximum number of particles, we consider the trap parameters and the results given by Roberts et al. [Phys. Rev. Lett. 86, 4211 (2001)]. However, this study can be easily transferred to other trap geometries to estimate anharmonic effects.Comment: Total of 5 pages, 3 figures and 1 table. To appear in Phys. Rev.

Bose-Einstein condensation with magnetic dipole-dipole forces

Ground-state solutions in a dilute gas interacting via contact and magnetic dipole-dipole forces are investigated. To the best of our knowledge, it is the first example of studies of the Bose-Einstein condensation in a system with realistic long-range interactions. We find that for the magnetic moment of e.g. chromium and a typical value of the scattering length all solutions are stable and only differ in size from condensates without long-range interactions. By lowering the value of the scattering length we find a region of unstable solutions. In the neighborhood of this region the ground state wavefunctions show internal structures not seen before in condensates. Finally, we find an analytic estimate for the characteristic length appearing in these solutions.Comment: final version, 4 pages, 4 figure

Instability of a Bose-Einstein Condensate with Attractive Interaction

We study the stability of a Bose-Einstein condensate of harmonically trapped atoms with negative scattering length, specifically lithium 7. Our method is to solve the time-dependent nonlinear Schrodinger equation numerically. For an isolated condensate, with no gain or loss, we find that the system is stable (apart from quantum tunneling) if the particle number N is less than a critical number N_c. For N > N_c, the system collapses to high-density clumps in a region near the center of the trap. The time for the onset of collapse is on the order of 1 trap period. Within numerical uncertainty, the results are consistent with the formation of a "black hole" of infinite density fluctuations, as predicted by Ueda and Huang. We obtain numerically N_c approximately 1251. We then include gain-loss mechanisms, i.e., the gain of atoms from a surrounding "thermal cloud", and the loss due to two- and three-body collisions. The number N now oscillates in a steady state, with a period of about 145 trap periods. We obtain N_c approximately 1260 as the maximum value in the oscillations.Comment: Email correspondence to [email protected] ; 18 pages and 9 EPS figures, using REVTeX and BoxedEPS macro