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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Improving finite element methods for fabricated structures

Barron, James Richard January 2000 (has links)
No description available.

Advanced integrated helicopter flight simulator cockpit design

Elias, Joerg 08 1900 (has links)
No description available.

Experimental evaluation of the performance and robustness of advanced rotor control schemes

Mullen, Gerald John January 1998 (has links)
No description available.

Real-time helicopter modelling using transputers

Lawes, Stephen Thomas January 1994 (has links)
No description available.

Digital automatic flight control systems for advanced rotorcraft : an analysis framework

Gee, Alan David January 2000 (has links)
No description available.

Non-linear optimisation problems in active control

Baek, Kwang-Hyun January 1996 (has links)
No description available.

An experimental and a theoretical investigation of rotor pitch damping using a model rotor

Sotiriou, C. P. January 1990 (has links)
No description available.

Adaptive nonlinear modelling of the W30 helicopter using neural networks

Thomas, Stephen Malcolm January 1996 (has links)
No description available.

A design study for a compound helicopter featured with a convertible prop/rotor

Mostafa, A. January 1989 (has links)
A compound helicopter is a hybrid vehicle, fundamentally a helicopter. It uses an auxiliary lift and propulsion device(s) in order to eliminate the lifting rotor high speed limitation of retreating blade stall effects, thus allowing flight characteristics comparable in many respects to those of fixed-wing aircraft. The primary objective of this thesis was to perform a design study investigating the validity of the concept of compounding, then selecting and designing a shaft-driven single compound helicopter intended for use as a ground support and anti-tank VTOL aircraft. The selection included a complete parametric and sizing analysis which were based on three defined maj or mission requirements: a maximum forward speed of 250 knots; payload of 1500 lb and cruising endurance of 3 hours at 225 knots. Of the many configurations studied, a single-rotor compound helicopter featured with convertible tail prop/rotor was found to be the most suitable for the intended application. Stability/control characteristics and performance capability of the designed aircraft were found to meet or exceed military specifications and flying quality requirements. structure, dynamics and cost analysis were considered to be beyond the scope of the design study.

Study of compressible flow through a rotating duct

Karpatne, Anand 17 September 2015 (has links)
Several rotorcraft applications such as circulation control and tip jet driven rotors involve internal spanwise flow along the interior of a rotor blade. This dissertation describes a quasi 1-D numerical model of unsteady flow through a duct rotating about one end along with experimental validations. The numerical model is suitable for inclusion in the conceptual design stage for helicopter rotor blades with internal spanwise flow. To this end, centrifugal as well as coriolis effects, frictional losses, duct sweep and time-dependent duct boundary conditions are modeled, and a spanwise flow control valve can be included. One dimensional Euler equations are solved inside the duct using a finite volume formulation in which the advective fluxes are approximated using the Advective Upwind Splitting Method (AUSM). The model is used to explore the behavior of flow inside a 2 m long duct with a circular crosssection, rotating at tip speeds of up to 260 m/s. In the inviscid limit, at a rotor tip speed of 213 m/s, the model predicted the evolution of a shock which showed periodic oscillations with a time period of approximately 17.5 rotor revolutions. However, when friction was included, a shock did not form until the rotor tip speed was ~ 260 m/s. The effects of suddenly opening a flow control valve at different spanwise stations, x [subscript valve] = 0.0R, x [subscript valve] = 0.5R and x [subscript valve] = R, were also studied numerically. Predictions of both steady and transient flow properties from this model are validated with experiments conducted on a 1.32 m long cylindrical duct, with a cross-sectional diameter of 52 mm, rotating at speeds of upto 1050 RPM (Tip Speed = 145 m/s). Spanwise pressure distribution, duct velocity, temperature, hub forces and moments results from the numerical model showed good correlation with experiments. Considerable internal mass flow rate (~ 0.3 kg/s) was also observed. In the presence of a time-varying valve at the inlet, transient spanwise pressure variations showed periodic fluctuations in pressure which diminished once the valve was fully open. The quasi 1-D model was found to be a much faster computational tool than any conventional 3-D CFD solver to study spanwise flow inside rotor blades. The experiments revealed key information about pressure at the duct's outlet. It was observed that when the duct's inlet is closed, the duct's outlet pressure is less than its ambient value. The knowledge of these boundary conditions is essential in modeling flow through rotating ducts. For more accuracy, the current internal flow solver could be coupled with an external flow code to iteratively obtain boundary conditions at their interface.

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