407 research outputs found
Bifurcation tailoring of nonlinear systems
No full textWe discuss a novel approach to control bifurcations in nonlinear systems. The aim of bifurcation tailoring is to design an appropriate control law such that the controlled system has a desired bifurcation diagram. After describing two open-loop bifurcation tailoring techniques, this paper proposes two alternative modified bifurcation tailoring methods based on the use of the Newton-flow algorithm and the so-called Minimal Control Synthesis adaptive control strategy. The novel technique is applied to the Duffing system as an illustration example
Continuation based control of aircraft dynamics
No full textThis paper presents an approach to controlling nonlinear aircraft dynamics over a wide range of parameter variation by incorporating bifurcation analysis and numerical continuation methods into the controller design process. This is a significant improvement over the standard control approach of interpolating between a few design points in the flight envelope. Adaptive control in the form of the minimal control synthesis (MCS) is shown to improve the robustness of the controller in the presence of modelling uncertainties. The above methods are applied to a second-order complex nonlinear highly maneuverable aircraft model
On-line Bifurcation tailoring: an application to a nonlinear aircraft model
No full textBifurcation tailoring is a novel control technique aimed at changing the entire bifurcation diagram of a given nonlinear system to some desired one. Bifurcation tailoring was successfully carried out on a second order nonlinear highly manoeuvrable aircraft model so as to control the angle of attack to an arbitrary prescribed bifurcation diagram under the variation of elevator. On-line feedforward scheduling was carried out using a Newton Flow method, and feedback stabilisation was provided by an adaptive control strategy known as the Minimal Control Synthesis (MCS)
Wind tunnel manoeuvre rig:a multi-DOF test platform for model aircraft
No full textThis paper presents recent progress in the development of a novel multi-degree-of-freedom dynamic manoeuvre rig aimed at investigation of aircraft model nonlinear and time dependent aerodynamics in the wind tunnel. The purpose and characteristics of the rig are first described, along with a description of the data acquisition, processing and presentation system. The dynamic manoeuvre rig capabilities are demonstrated via a series of experiments involving a wind tunnel model aircraft in a closed section low-speed wind tunnel. First, an experiment illustrating low-speed wind tunnel aerodynamic model identification is presented. Then, examples of experiments involving real-time control of the rig/aircraft model are shown; these are evaluated in terms of testing productivity with a focus on the development and design of aircraft control laws
A bifurcation study to guide the design of a landing gear with a combined uplock/downlock mechanism
No full textThis paper discusses the insights that a bifurcation analysis can provide when designing mechanisms. A model, in the form of a set of coupled steady-state equations, can be derived to describe the mechanism. Solutions to this model can be traced through the mechanism's state versus parameter space via numerical continuation, under the simultaneous variation of one or more parameters. With this approach, crucial features in the response surface, such as bifurcation points, can be identified. By numerically continuing these points in the appropriate parameter space, the resulting bifurcation diagram can be used to guide parameter selection and optimization. In this paper, we demonstrate the potential of this technique by considering an aircraft nose landing gear, with a novel locking strategy that uses a combined uplock/downlock mechanism. The landing gear is locked when in the retracted or deployed states. Transitions between these locked states and the unlocked state (where the landing gear is a mechanism) are shown to depend upon the positions of two fold point bifurcations. By performing a two-parameter continuation, the critical points are traced to identify operational boundaries. Following the variation of the fold points through parameter space, a minimum spring stiffness is identified that enables the landing gear to be locked in the retracted state. The bifurcation analysis also shows that the unlocking of a retracted landing gear should use an unlock force measure, rather than a position indicator, to de-couple the effects of the retraction and locking actuators. Overall, the study demonstrates that bifurcation analysis can enhance the understanding of the influence of design choices over a wide operating range where nonlinearity is significant
Geometric nonlinearities of aircraft systems
No full textNonlinearities due to geometric effects, in particular, via angular variables that are not small, are important for aircraft operation. Geometric nonlinearities have a strong effect on the dynamics of the aircraft system under consideration, and they are especially pronounced in aircraft ground operations. As a concrete example we consider here the effect of a non-zero rake angle on the dynamics of a nose landing gear. More specifically, we use tools from bifurcation theory to investigate the stability of the straight-rolling motion during a take-off run
Bifurcation Tailoring via Newton-flow aided adaptive control
No full textThe aim of bifurcation tailoring is to design an appropriate control law such that the controlled system has a desired bifurcation diagram. After describing two open-loop bifurcation tailoring techniques, this paper proposes a new open-loop plus close-loop bifurcation tailoring method based on a combination of the Newton-flow algorithm and the minimal control synthesis (MCS) adaptive control strategy. This method is applied to the Duffing system as an illustrative example
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