Optimal Dirichlet boundary control problems of high-lift configurations with control and integral state constraints [Elektronische Ressource] / Christian John. Betreuer: Fredi Tröltzsch

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• Mathematics

Informations

• Publié par: technische_universitat_berlin
• Publié le: 01 janvier 2011
• Nombre de lectures: 10
• Langue: English
• Poids de l'ouvrage: 10 Mo

Extrait

Optimal Dirichlet boundary control
problems of high-lift configurations with
control and integral state constraints
vorgelegt von
Diplom-Wirtschaftsmathematiker
Dipl.-Math.oec. Christian John
aus Berlin
Von der Fakultät II - Mathematik und Naturwissenschaften
der Technischen Universität Berlin
zur Erlangung des akademischen Grades
Doktor der Naturwissenschaften
Dr. rer. nat.
genehmigte Dissertation
Promotionsausschuss:
Vorsitzender: Prof. Dr. John M. Sullivan
Gutachter: Prof. Dr. Fredi Tröltzsch
Gutachter: Prof. Dr. Arnd Rösch
Tag der wissenschaftlichen Aussprache: 13.07.2011
Berlin 2011
D 83iiAbstract
This thesis investigates optimal control problems related to Navier-Stokes
equations. We investigate two control problems related to the aerodynamic
optimization of flows around airfoils in high-lift configurations.
The first issue is the steady state maximization of lift subject to restric-
tions on the drag. This leads to a Dirichlet boundary control problem for
thestationaryNavier-Stokesequationswithconstrainedcontrolfunctionsbe-
2 2
longing to L under an integral state constraint. The control space L makes
it necessary to deal with very weak solutions of the Navier-Stokes equations
andbecauseofthelowregularityofcontrolandstate, wereformulatethecost
functional and the integral state constraint. We derive first-order necessary
and second-order sufficient optimality conditions and treat the problem nu-
merically by direct solution of the associated nonsmooth optimality system
and additionally by an SQP-method, which convergence we proved.
The second part is based on ak-!-Wilcox98 turbulence model, describ-
ing the nonstationary behavior of the fluid closer to the reality. To deal with
thecurseofdimension, wediscussareduced-ordermodel(ROM)byadapting
a small system of ODEs to solutions computed with the full model. Based
on this ROM, we investigate an optimal control problem theoretically and
numerically.
Acknowledgment
I think it is impossible to write a doctoral dissertation without some kind of
support. I am grateful to the DFG (SFB 557 ’Control of complex turbulent
shear flows’) supporting me in the first three years financially and to the
FAZIT-Stiftung for their financial support in the last 9 months.
My first and biggest gratitude goes to my supervisor Prof. Dr. Fredi
Tröltzsch for the interesting topic, his helpful advice and his personality in
general. I thank Dr. Daniel Wachsmuth, who worked with me together for
about 2 years when i started my project at the TU Berlin, for introducing me
intothetopicofoptimalcontrolofNavier-Stokesequations, hisinterestinmy
work and many helpful inspirations. Many thanks go to my colleagues in the
research group ’Optimization on PDEs’ at the TU Berlin, especially Kristof
Altmann for introducing me into COMSOL Multiphysics, and to Prof. Dr.
Arnd Rösch for his willingness to review this thesis.
iiiFurthermore, my gratitude to B.R. Noack and M. Schlegel for the good
and successful cooperation. They introduced me into the topic of proper or-
thogonal decomposition and reduced-order modeling and supported me with
both words and deeds. I also want to thank M. Luchtenburg for explaining
me his reduced-order model, M. Nestler for his helpful assistance and the
group of Prof. Thiele, especially B. Günther and A. Carnarius, for providing
me with simulations of the URANS system.
Finally, i thank my friends and my family.
ivContents
1 Introduction 1
2 The steady-state Navier-Stokes equation 7
2.1 Function spaces . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 The Stokes equations . . . . . . . . . . . . . . . . . . . . . . . 11
2.3 Weak formulation . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.4 Very weak formulation . . . . . . . . . . . . . . . . . . . . . . 15
2.4.1 More regular solutions . . . . . . . . . . . . . . . . . . 17
2.4.2 Regularity assumption . . . . . . . . . . . . . . . . . . 19
3 The optimal control problem 21
3.1 Reformulation of the boundary integrals . . . . . . . . . . . . 21
3.2 Further reformulation of the boundary integrals . . . . . . . . 22
3.3 The optimal control problem . . . . . . . . . . . . . . . . . . . 24
3.3.1 Existence of solutions . . . . . . . . . . . . . . . . . . . 24
4 Optimality conditions 29
4.1 First order necessary optimality conditions . . . . . . . . . . . 29
4.2 Second-order sufficient optimality condition . . . . . . . . . . 33
4.3 Finite-dimensional control set . . . . . . . . . . . . . . . . . . 39
4.4 sufficient optimality conditions for the finite-
dimensional case . . . . . . . . . . . . . . . . . . . . . . . . . 44
5 Numerical investigations 47
5.1 One-shot approach . . . . . . . . . . . . . . . . . . . . . . . . 47
5.1.1 Numerical results . . . . . . . . . . . . . . . . . . . . . 49
5.2 SQP-method . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
5.2.1 The SQP-method for our problem . . . . . . . . . . . . 58
5.2.2 Gradient-projection method . . . . . . . . . . . . . . . 65
5.2.3 Example . . . . . . . . . . . . . . . . . . . . . . . . . . 66
vCONTENTS
6 Convergence of the SQP-method 69
6.1 Generalized equations . . . . . . . . . . . . . . . . . . . . . . . 71
6.2 Perturbed optimization problem . . . . . . . . . . . . . . . . . 76
6.3 A modified problem . . . . . . . . . . . . . . . . . . . . . . . . 79
6.3.1 Existence of a solution . . . . . . . . . . . . . . . . . . 79
6.3.2 Lipschitz stability . . . . . . . . . . . . . . . . . . . . . 80
6.4 Strong regularity of the original perturbed problem . . . . . . 85
7 The nonstationary case 89
7.1 Model reduction . . . . . . . . . . . . . . . . . . . . . . . . . . 91
7.2 Proper orthogonal decomposition POD . . . . . . . . . . . . . 92
8 Reduced-order model (ROM) 103
8.1 A generalized model . . . . . . . . . . . . . . . . . . . . . . . 106
8.1.1 Mean-field theory . . . . . . . . . . . . . . . . . . . . . 106
8.1.2 Galerkin model . . . . . . . . . . . . . . . . 110
8.2 Modifications on the reduced-order model . . . . . . . . . . . 117
8.2.1 Filtering of the POD modes and coefficients . . . . . . 117
8.2.2 Parameter calibration . . . . . . . . . . . . . . . . . . . 124
8.3 Computation of lift . . . . . . . . . . . . . . . . . . . . . . . . 129
8.4 Numerical investigation . . . . . . . . . . . . . . . . . . . . . . 130
9 The optimal control problem 135
9.1 First-order necessary optimality conditions . . . . . . . . . . . 136
9.2 Numerical investigation . . . . . . . . . . . . . . . . . . . . . . 139
10 Conclusion 145
11 Zusammenfassung 147
viChapter 1
Introduction
In this thesis, we study optimal control problems related to Navier-Stokes
equations, describing the motion of fluid. We investigate minimizations of
functionals subject to state equations. The objective functionals depend on
the velocity field u, the pressure p and the control function g:
Our main concern is maximization the lift of an airplane, while drag
remains beyond a given threshold. Therefore, we consider an objective func-
tional J(u;p;g) characterizing the lift, the Navier-Stokes equations as state
equations and a constraint on the drag.
In given literature, there are two different approaches to get influence on
the flow around a body. The first one is the possibility of passive control.
There are several possibilities of passive control, e.g. passive blowing,
roughness and shaping. Passive noise control devices include shields of rigid
and compliant walls, mufflers, silencers, resonators and absorbent materials,
see [43] for more details. The idea behind most of them is to reduce vortices
and make the airstream around the wing smoother.
The second ansatz is active flow control, which was investigated in partic-
ular by the SFB 557 ’Control of complex turbulent shear flows’. Here, little
slits are installed on a part of the wing, where suction and blowing of air is
possible to reduce vortices.
Generally, flow control is a research field gaining a lot of interest in both
academic research and industry. It is researched by engineers (experimen-
tal and computation fluid dynamics), mathematicians (control theory and
optimization) and physicists.
In this work, the following optimal flow control problem is considered: ac-
tive control of the flow of a fluid around an aircraft by means of suction and
blowing on the wing to influence the resulting lift and drag. The associated
background of applications in fluid mechanics, active separation control, was
the subject of various papers written from an engineering point of view and
1CHAPTER 1. INTRODUCTION
has been proven to be effective in experiments as well as simulations. We
only mention [17, 19, 87, 88, 89, 112], whose considerations are close to our
setting, see Chapter 7 to 9.
The first part of this thesis deals with the steady-state problem. Here, we
assume a low Reynolds number so that we avoid the discussion of turbulence.
Furthermore, we consider a simplified control model, which is composed of
thecostfunctional, thesteady-stateNavier-Stokesequations, andconstraints
on the control function as well as the state, for a mathematical investigation.
First, the steady-state Navier-Stokes equations, describing the motion of the
fluid around the wing, are investigated and we clarify the following que