Difference between revisions of "F-8 aircraft"

F-8 aircraft
State dimension:	1
Differential states:	3
Discrete control functions:	1
Interior point equalities:	6

Revision as of 10:46, 17 April 2016

The F-8 aircraft control problem is based on a very simple aircraft model. The control problem was introduced by Kaya and Noakes and aims at controlling an aircraft in a time-optimal way from an initial state to a terminal state.

The mathematical equations form a small-scale ODE model. The interior point equality conditions fix both initial and terminal values of the differential states.

The optimal, relaxed control function shows bang bang behavior. The problem is furthermore interesting as it should be reformulated equivalently.

Mathematical formulation

For $t \in [0, T]$ almost everywhere the mixed-integer optimal control problem is given by

$\begin{array}{llcl} \displaystyle \min_{x, w, T} & T \\[1.5ex] \mbox{s.t.} & \dot{x}_0 &=& -0.877 \; x_0 + x_2 - 0.088 \; x_0 \; x_2 + 0.47 \; x_0^2 - 0.019 \; x_1^2 - x_0^2 \; x_2 + 3.846 \; x_0^3 \\ &&& - 0.215 \; w + 0.28 \; x_0^2 \; w + 0.47 \; x_0 \; w^2 + 0.63 \; w^3 \\ & \dot{x}_1 &=& x_2 \\ & \dot{x}_2 &=& -4.208 \; x_0 - 0.396 \; x_2 - 0.47 \; x_0^2 - 3.564 \; x_0^3 \\ &&& - 20.967 \; w + 6.265 \; x_0^2 \; w + 46 \; x_0 \; w^2 + 61.4 \; w^3 \\ & x(0) &=& (0.4655,0,0)^T, \\ & x(T) &=& (0,0,0)^T, \\ & w(t) &\in& \{-0.05236,0.05236\}. \end{array}$

$x_0$ is the angle of attack in radians, $x_1$ is the pitch angle, $x_2$ is the pitch rate in rad/s, and the control function $w = w(t)$ is the tail deflection angle in radians. This model goes back to Garrard[Garrard1977]Author: Garrard, W.L.; Jordan, J.M.
Journal: Automatica
Pages: 497--505
Title: Design of Nonlinear Automatic Control Systems
Volume: 13
Year: 1977
.

In the control problem, both initial and terminal values of the differential states are fixed.

Reformulation

The control w(t) is restricted to take values from a finite set only. Hence, the control problem can be reformulated equivalently to

$\begin{array}{llcl} \displaystyle \min_{x, w, T} & T \\[1.5ex] \mbox{s.t.} & \dot{x}_0 &=& -0.877 \; x_0 + x_2 - 0.088 \; x_0 \; x_2 + 0.47 \; x_0^2 - 0.019 \; x_1^2 - x_0^2 \; x_2 + 3.846 \; x_0^3 \\ &&& - \left( 0.215 \; \xi - 0.28 \; x_0^2 \; \xi - 0.47 \; x_0 \; \xi^2 - 0.63 \; \xi^3 \right) \; w \\ &&& - \left( - 0.215 \; \xi + 0.28 \; x_0^2 \; \xi - 0.47 \; x_0 \; \xi^2 + 0.63 \; \xi^3 \right) \; (1 - w) \\ & &=& -0.877 \; x_0 + x_2 - 0.088 \; x_0 \; x_2 + 0.47 \; x_0^2 - 0.019 \; x_1^2 - x_0^2 \; x_2 + 3.846 \; x_0^3 \\ &&& + 0.215 \; \xi - 0.28 \; x_0^2 \; \xi + 0.47 \; x_0 \; \xi^2 - 0.63 \; \xi^3 \\ &&& - \left( 0.215 \; \xi - 0.28 \; x_0^2 \; \xi - 0.63 \; \xi^3 \right) \; 2 w \\ & \dot{x}_1 &=& x_2 \\ & \dot{x}_2 &=& -4.208 \; x_0 - 0.396 \; x_2 - 0.47 \; x_0^2 - 3.564 \; x_0^3 \\ &&& - \left( 20.967 \; \xi - 6.265 \; x_0^2 \; \xi -46 \; x_0 \; \xi^2 - 61.4 \; \xi^3 \right) \; w \\ &&& - \left( - 20.967 \; \xi + 6.265 \; x_0^2 \; \xi -46 \; x_0 \; \xi^2 + 61.4 \; \xi^3 \right) \; (1 - w) \\ & &=& -4.208 \; x_0 - 0.396 \; x_2 - 0.47 \; x_0^2 - 3.564 \; x_0^3 \\ &&& + 20.967 \; \xi - 6.265 \; x_0^2 \; \xi + 46 \; x_0 \; \xi^2 - 61.4 \; \xi^3 \\ &&& - \left( 20.967 \; \xi - 6.265 \; x_0^2 \; \xi - 61.4 \; \xi^3 \right) \; 2 w \\ & x(0) &=& (0.4655,0,0)^T, \\ & x(T) &=& (0,0,0)^T, \\ & w(t) &\in& \{0,1\}, \end{array}$

with $\xi = 0.05236$ . Note that there is a bijection between optimal solutions of the two problems.

Reference solutions

We provide here a comparison of different solutions reported in the literature. The numbers show the respective lengths $t_i - t_{i-1}$ of the switching arcs with the value of $w(t)$ on the upper or lower bound (given in the second column). Claim denotes what is stated in the respective publication, Simulation shows values obtained by a simulation with a Runge-Kutta-Fehlberg method of 4th/5th order and an integration tolerance of $10^{-8}$ .

Arc	w(t)	Lee et al.[Lee1997a]Author: Lee, H.W.J.; Teo, K.L.; Rehbock, V.; Jennings, L.S. Journal: Dynamic Systems and Applications Pages: 243--262 Title: Control Parametrization Enhancing Technique for Time-Optimal Control Problems Volume: 6 Year: 1997	Kaya[Kaya2003]Author: C.Y. Kaya; J.L. Noakes Journal: Journal of Optimization Theory and Applications Pages: 69--92 Title: A Computational Method for Time-Optimal Control Volume: 117 Year: 2003	Sager[Sager2005]Address: Tönning, Lübeck, Marburg Author: S. Sager Editor: ISBN 3-89959-416-9 Publisher: Der andere Verlag Title: Numerical methods for mixed--integer optimal control problems Url: http://mathopt.de/PUBLICATIONS/Sager2005.pdf Year: 2005	Schlueter/ Gerdts	Sager
1	1	0.00000	0.10292	0.10235	0.0	1.13492
2	0	2.18800	1.92793	1.92812	0.608750	0.34703
3	1	0.16400	0.16687	0.16645	3.136514	1.60721
4	0	2.88100	2.74338	2.73071	0.654550	0.69169
5	1	0.33000	0.32992	0.32994	0.0	0.0
6	0	0.47200	0.47116	0.47107	0.0	0.0
Claim: Infeasibility	-	1.00E-10	7.30E-06	5.90E-06	3.29169e-06	2.21723e-07
Claim: Objective	-	6.03500	5.74217	5.72864	4.39981	3.78086
Simulation: Infeasibility	-	1.75E-03	1.64E-03	5.90E-06	3.29169e-06	2.21723e-07
Simulation: Objective	-	6.03500	5.74218	5.72864	4.39981	3.78086

The best known optimal objective value of this problem given is given by $T = 3.78086$ . The corresponding solution is shown in the rightmost plot. The solution of bang-bang type switches three times, starting with $w(t) = 1$ .

Reference solution plots
Locally optimal relaxed control on a coarse control discretization grid and corresponding differential states.
Locally optimal relaxed control on a fine, adaptively chosen control discretization grid and corresponding differential states.
Integer control and corresponding differential states from Sager[Sager2005]Address: Tönning, Lübeck, Marburg
Author: S. Sager
Editor: ISBN 3-89959-416-9
Publisher: Der andere Verlag
Title: Numerical methods for mixed--integer optimal control problems
Url: http://mathopt.de/PUBLICATIONS/Sager2005.pdf
Year: 2005
.
Integer control and corresponding differential states from Schlueter/ Gerdts solution.
Best known integer control and corresponding differential states from Sager solution.

jModelica

Objective : 5.12799232 infeasibility : 6.2235588037251599e-10

Obtained solution plots
(Probably sub-)Optimal control.
Corresponding differential states.

Source Code

Model descriptions are available in

Variants

a prescribed time grid for the control function, see F-8 aircraft (AMPL),

Miscellaneous and Further Reading

See [Kaya2003]Author: C.Y. Kaya; J.L. Noakes
Journal: Journal of Optimization Theory and Applications
Pages: 69--92
Title: A Computational Method for Time-Optimal Control
Volume: 117
Year: 2003
and [Sager2005]Address: Tönning, Lübeck, Marburg
Author: S. Sager
Editor: ISBN 3-89959-416-9
Publisher: Der andere Verlag
Title: Numerical methods for mixed--integer optimal control problems
Url: http://mathopt.de/PUBLICATIONS/Sager2005.pdf
Year: 2005
for details.

References

[Garrard1977]	Garrard, W.L.; Jordan, J.M. (1977): Design of Nonlinear Automatic Control Systems. Automatica, 13, 497--505
[Kaya2003]	C.Y. Kaya; J.L. Noakes (2003): A Computational Method for Time-Optimal Control. Journal of Optimization Theory and Applications, 117, 69--92
[Lee1997a]	Lee, H.W.J.; Teo, K.L.; Rehbock, V.; Jennings, L.S. (1997): Control Parametrization Enhancing Technique for Time-Optimal Control Problems. Dynamic Systems and Applications, 6, 243--262
[Sager2005]	S. Sager (2005): Numerical methods for mixed--integer optimal control problems. (%edition%). Der andere Verlag, Tönning, Lübeck, Marburg, %pages%

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 </gallery>
-=== Optimica ===
+=== jModelica ===
 Objective     : 5.12799232

Difference between revisions of "F-8 aircraft"

Revision as of 10:46, 17 April 2016

Contents

Mathematical formulation

Reformulation

Reference solutions

jModelica

Source Code

Variants

Miscellaneous and Further Reading

References

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