Over the past two decades. bifurcation and continuation methods have emerged as efficient tools for prediction. and control of flight instabilities, Bifurcation phenomena have been associated with nonlinear behaviour ...
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Over the past two decades. bifurcation and continuation methods have emerged as efficient tools for prediction. and control of flight instabilities, Bifurcation phenomena have been associated with nonlinear behaviour of aircraft in actual flight tests. and the critical control combinations. which signify onset of instabilities. have been identified for almost all generations of modern fighter aircraft. A standard bifurcation analysis procedure has been used in the past. In this paper, the bifurcation theory. relevant to preliminary bifurcation analysis of nonlinear aircraft dynamics. has been introduced. and a stepwise methodology used in a standard bifurcation analysis procedure has been illustrated with an application to open-loop dynamics of an F-18/HARV model in landing configuration. Further, an example manoeuvre is constructed. and numerical time simulations of an F-18/HARV model in this manoeuvre is carried Out to validate the predictions from the bifurcation analysis. Numerical time simulation results confirm the onset of nonlinear behaviour at critical control combinations identified in bifurcation analysis of the aircraft model, Thus. bifurcation methods, in conjunction with selective numerical simulations. can be extremely useful in the design, development. evaluation. and flight training phases of a fighter aircraft development programme.
This study proposes a novel multi-rate model predictive control (MPC) scheme for linear discrete-time systems subject to input constraints. The proposed scheme consists of two control layers, acting at two different t...
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This study proposes a novel multi-rate model predictive control (MPC) scheme for linear discrete-time systems subject to input constraints. The proposed scheme consists of two control layers, acting at two different timescales. At a slow timescale, the outputs associated with the slow dynamics are steered to their reference values while at a fast timescale, a shrinking horizon MPC regulator is designed to refine the control action computed at the slow timescale. The proposed control scheme shows to be particularly useful, not only to control systems with different open-loop dynamics but also in cases when the controlled variables are required to have different responsiveness in a closed loop. Simulation results on a fire tube boiler example are reported, which indeed show that different dynamics can be efficiently imposed on the controlled variables, i.e. the boiler pressure and the water level, in the presence of variations of the disturbance represented by the steam output flow rate.
The paper describes the application of indirect identification methods to obtain a state-space representation of the open-loop dynamics of a nonlinear laboratory model turbogenerator, which is operated in closed loop....
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The paper describes the application of indirect identification methods to obtain a state-space representation of the open-loop dynamics of a nonlinear laboratory model turbogenerator, which is operated in closed loop. The model structure and selection of variables are determined on the basis of simulation studies and residual analysis, and a recursive instrumental variables technique is employed for online parameter identification. The identified models were used in the design of optimal controllers for the turbogenerator, which have been tested in the laboratory and shown to be most effective. It has also been established that the process of online identification does not reduce the stability of the system.
The classic two-state continuous stirred tank reactor (CSTR) model has been the focus of much of the previous research on exothermic reactor operation. One assumption of this model is that the cooling jacket temperatu...
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The classic two-state continuous stirred tank reactor (CSTR) model has been the focus of much of the previous research on exothermic reactor operation. One assumption of this model is that the cooling jacket temperature dynamics are negligible, hence the cooling jacket temperature is the manipulated input (instead of the cooling jacket flowrate) for feedback control of reactor temperature. The influence of process design parameters on the open-loop behavior of a three-state CSTR model (which incorporates an energy balance around the cooling jacket) is considered in this paper. Elementary catastrophe theory is used to study the effect of process parameters on the steady-state multiplicity of the three-state CSTR model. We demonstrate the existence of disjoint bifurcations associated with infeasible reactor operation regions. Reactor scaleup is shown to have an effect on the presence of these infeasible reactor operation regions. A multiple time-scale perturbation analysis is used to understand the effect of reactor design on the oscillation amplitude of the three-state CSTR model at a Hopf bifurcation point.
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