Boundary Control of Linear Evolution PDEs  Continuous and Discrete  Jan Marthedal Rasmussen
 Abstract  Consider a partial di erential equation (PDE) of evolution type, such as the wave equation or the heat equation. Assume now that you can influence the behavior of the solution by setting the boundary conditions as you please. This is boundary control in a broad sense. A substantial amount of literature exists in the area of theoretical results concerning control of partial differential equations. The results have included existence and uniqueness of controls, minimum time requirements, regularity of domains, and many others. Another huge research field is that of control theory for ordinary di erential equations. This field has mostly concerned engineers and others with practical applications in mind.
This thesis makes an attempt to bridge the two research areas. More specifically, we make finite dimensional approximations to certain evolution PDEs, and analyze how properties of the discrete systems resemble the properties of the continuous system. A common framework in which the continuous systems are formulated will be provided. The treatment includes many types of linear evolution PDEs and boundary conditions. We also consider di erent types of controllability, such as approximate, null and exact controllability. We will consider discrete systems with a viewpoint similar to that used for the continuous systems. Most importantly, we study what is required of a discretization scheme in order for computed control functions to converge to the true, continuous, control function. Examples exist for convergent discretization schemes for which divergence of the computed controls occur. We dig deeper for three specific cases: The heat equation, the wave equation, and a linear system of thermoelasticity. Different aspects of the theory are exemplified through these case studies. We finally consider how to e ciently implement computer programs for computing controls in practice.  Type  Ph.D. thesis [Academic thesis]  Year  2004  Publisher  Informatics and Mathematical Modelling, Technical University of Denmark, DTU  Address  Richard Petersens Plads, Building 321, DK2800 Kgs. Lyngby  Series  IMMPHD2004139  Note  Supervised by Prof. Per Christian Hansen, IMMDTU, and and Assoc.Prof. Michael Pedersen, MATDTU  Electronic version(s)  [pdf] [ps]  BibTeX data  [bibtex]  IMM Group(s)  Scientific Computing 
