Special Session 23: New Developments in Nonlinear Partial Differential Equations and Control Theory Irena Lasiecka, University of Virginia, Charlottesville, USA Grozdena Todorova, University of Tennessee, Knoxville, USA This session will focus on qualitative behavior of solutions to nonlinear evolution equations that are motivated by strong applications in mechanics and physics. Particular examples include: nonlinear wave equations, nonlinear Shrodinger equations, nonlinear plate equations, Navier Stokes and Euler equations, Gunzburg Landau equations etc. In addition to classical issues of wellposedness of nonlinear problems, of particular interest to the session are questions related to asymptotic (in time) behavior of solutions, stability/instability, formation and propagation of singularities, regularity of solutions. Both controlled and uncontrolled , forward and inverse dynamics will be considered. In fact, new developments in control theory of nonlinear PDE’s bring forward several open questions as well as techniques that could be used in order to forge a desirable (from the point of view of applications) outcome of the dynamics. These include prob- lems such as stabilization, controllability, formation of attractors /inertial manifolds, optimization, identification and reconstruction of the data such as initial conditions or sources in the equations. However, these techniques depend heavily on a deep understanding of a free- uncontrolled dynamics. Thus, the aim of the session is to bring together both constituencies, so people working on different aspects of mathematical properties of solutions to nonlinear evo- lutionary dynamics could exchange expertize and benefit from it. Particular emphasis will be given to new techniques and methodologies developed for classes of problems under consideration. ¡! ¥ ¦ ¥ á Controllability Properties of Nonlinear Rotation-Free The central problem of AeroElasticity is an endemic in- Thermoelastic Systems stability flutter that occurs at high enough airspeed in subsonic flight. Currently almost all the work is compu- George Avalos tational. In contrast we retain the full continuum models University of Nebraska-Lincoln, USA and formulate it as a boundary value problem for the [email protected] Euler Full Potential Equation or the simpler quasilinear Transonic Small Disturbance Potential Equation. The flutter speed is a Hopf Bifurcation point for a non-linear In this talk, we provide results of local and global con- convolution/evolution equation in a Hilbert Space, and is trollability (exact and global) for 2-D nonlinear thermoe- determined by the linearized equations. The latter formu- lastic systems, in the absence of rotational inertia. We will lates as Neumann type problem in Lp-spaces, 1 < p < 2, present results pertaining to the presence of both Lipschitz and the solution involves the Possio Singular Integral and non-Lipschitz nonlinearities. The plate component Equation. may be taken to satisfy either the clamped or higher order (and physically relevant) free boundary conditions. In the ¡! ¥ ¦ ¥ á accompanying analysis, critical use is made of sharp ob- servability estimates which obtain for the linearization of the thermoelastic plate. Moreover, key use is made of the Long-time behaviour of a coupled wave/plate PDE analyticity of the underlying linear semigroup. model Francesca Bucci ¡! ¥ ¦ ¥ á Universita’ degli Studi di Firenze, Italy francesca.bucci@unifi.it Modelling the Flutter Instability Problem of Aeroelas- ticity This talk will deal with long-time behaviour of a sys- tem of coupled second-order evolution equations with A. V. Balakrishnan nonlinear dampings. More precisely, the system com- UCLA, USA prises a semilinear wave equation on some smooth do- [email protected] main W ½ R3, and Berger’s plate model on a portion of the boundary of W, say G0; the coupling is strong as it takes place (through velocities traces) on G0. The talk between the numerical simulations of the effective equa- will focus on the issues of (i) existence of a global attrac- tions and the experimental results performed at the Texas tor for the dynamical system defined by the overall PDE Heart Institute in Houston showed excellent agreement. problem, and of (ii) dimension and smoothness of the We will discuss the existence of a solution to the effective attractor. Most results presented in the talk are jointly ob- free-boundary problem and the difficult challenges and tained with Igor Chueshov (Kharkov University, Ukraine) new insights that it brings towards the understanding of and Irena Lasiecka (University of Virginia). the fluid-structure interaction in blood flow. ¡! ¥ ¦ ¥ á ¡! ¥ ¦ ¥ á Weak and Regular Solutions for a Non-linear Shell Hadamard Wellposedness of a Two-Dimensional Problem with Small Finite Deflections Boussinesq Equation with Applications to Structural Acoustic Problems John Cagnol Pole Universitaire Leonard de Vinci, France Inger M. Daniels [email protected] University of Virginia, USA Irena Lasiecka and Catherine Lebiedzik [email protected] W.T. Koiter classifies shell problems according to the We consider a Boussinesq type equation defined on a order of magnitude of the deflection. The Small Finite smooth and bounded domain W 2 R2. It is shown that the Deflections, characterized by small displacement gradi- model admits ”finite energy” solutions that are Hadamard ents and by rotations whose squares do not exceed the well-posed. In particular, it is shown that nonlinear middle surface strain in order of magnitude leads a geo- restorative forces acting upon the plate prevent a finite- metrically nonlinear model discussed. In this prsentation time blow up weak solutions. we will consider a version of this model which is based The Boussinesq equation is then considered in a larger on the intrinsic shell modeling techniques introduced by context as a component of a structural acoustic model that Michel Delfour and Jean-Paul Zolesio.´ Mathematically describes oscillations of a pressure (acoustic wave equa- it takes the form of a set of coupled partial differential tion) in an acoustic chamber. By applying suitable control equations where the shell equation is a nonlinear, strongly mechanism on a flexible wall of the chamber, the goal of coupled with hyperbolic equations. We shall prove the the work is to show that the pressure (noise in an acous- existence of weak solutions as well as regular solutions of tic environment) can be effectively controlled. The pre- this system. sentation highlights the effects of a particular restorative force acting on the plate and interacting with an acous- ¡! ¥ ¦ ¥ á tic medium that is responsible for both wellposedness and control of the overall nonlinear model. Solutions to the hyperbolic-parabolic system modeling fluid-structure interaction in blood flow ¡! ¥ ¦ ¥ á Suncica Canic University of Houston, USA Modern Boundary Conditions [email protected] Andro Mikelic Jerome A. Goldstein University of Memphis, USA We will focus on a free-boundary problem for a quasi- [email protected] linear system of PDEs modeling blood flow in compliant Angelo Favini, Ciprian Gal, Gisele Ruiz Gldstein & arteries. The system of PDEs is of hyperbolic-parabolic Silvia Romanelli type. Hyperbolicity captures wave propagation in elastic arteries, and parabolicity describes the flow of a viscous Consider a parabolic (or hyperbolic) equation of the form incompressible fluid modeling blood flow. The system is obtained from the incompressible Navier-Stokes equa- D ju(t) = Au(t) tions coupled with the equations for a linearly elastic Koiter shell by using homogenization theory. The result- where D = d=dt, j = 1 or 2, A is an elliptic differential ing, effective model, captures the main features of blood operator in spatial variables x of order 2n, possibly non- flow in elastic arteries. More precisely, a comparison linear, acting in a domain R in Euclidean space. Recently much attention has been devoted to associated nonclassi- of general boundary conditions, Advances in Differential cal boundary conditions of the form Equations, to appear. 2. C. Gal, G.R. Goldstein, and J.A. Goldstein, Wave j D u + Bu = 0 on G;the boundary of R; j = 1;2 equations with nonlinear dynamic boundary conditions, in preparation. Au +Cu = 0onG; or others; B and C are operators of order less than 2n. ¡! ¥ ¦ ¥ á These dynamic, Wentzell, and acoustic boundary condi- tions will be briefly surveyed, from the perspective of On a proportional and derivative robust optimal feed- physical interpretation and wellposed problems. Exam- back for linear quadratic control problems ples discussed will include acoustic wave equations with both acoustic and nonlinear Wentzell boundary condi- Jacques Henry tions. INRIA, France [email protected] ¡! ¥ ¦ ¥ á linear-quadratic control prolem the derivation of the opti- Linear and Nonlinear Kinetic Boundary Conditions mal feedback is well known and goes back to the method for the Wave Equation of invariant embeding of R. Bellman. This embeding is done with respect to time and gives rise to a Riccati equa- Gisele R. Goldstein tion satisfied by the operator : state to adjoint state. It has University of Memphis, USA been showed that this invariant embeding can be viewed [email protected] as a continuous version of a Gauss LU block factorization Ciprian Gal and Jerome A. Goldstein of the optimality system (state - adjoint state). In this paper we want to investigate backwards what a QR factor- Of concern is the wave equation with kinetic boundary ization would mean in terms