A diploma thesis is not really a published paper. The reasons why it is added here to the list of my publications are twofold. First, it is a typical example of tasks performed in automatic control during that period. Second, I have learned a first essential systems engineering principle from this experience.
The subject of my diploma thesis dealt with the control of the magnetic vertical gap between the track and a high-speed magnetic alleviated train. The innovative idea was to consider the aerodynamic effects not just as disturbances, but to try to make some use of the aerodynamic forces for lifting the train in support of the magnetic force. As aerodynamic forces increase with speed approximately following a square function, this was a promising idea. The challenge for the automatic controller to fight against the disturbances following a square function at high speeds could be reduced. Less magnetic energy in the magnetic gap would mean less weight of the vehicle eventually. And, a smoother ride for the passengers seemed to be likely.
My role in the whole endeavour was to set up a first simple simulation model and to perform initial simulations applying optimal control theory on the basis of quadratic cost functions. From the research assistant I had got a differential equation system with a model of the magnet and another for the flight dynamics and some coupling terms between those models. Not all of the coupling terms had been defined yet, some were still under discussion involving a number of professors and further experts, and some seemed to be reasonable since they were undisputed.
The way this model had been generated seemed somewhat dubious to me. As a naïve novice, I tried to develop it using the mechanical and electro-magnetic laws from scratch. I ended up with a result that looked reasonable to me. But the solution was a bit different from the received simulation model. The most significant difference was that I came up with a differential equation system that was of the sixth order instead of the seventh order.
For good reasons, I am always sceptical regarding the results of my calculations. I repeated the deduction of the simulation model several times again. When I was convinced of the absence of nuisance errors in my algebraic calculations, I started to investigate why the solutions were different. The result of the analysis demonstrated that I was right. Just adding up the model of the magnet and the flight dynamic model does not work because the vertical force equation was defined twice independently from each other for the magnet and the flight dynamics.
When I introduced my solution to the research assistant, he was quite a bit reluctant to accept it. But despite the time and effort he had invested before, he advised me two weeks later to proceed on the basis of my solution.
Since then, I have been always rather cautious in just adding up partial models for defining a complete system model. It took not too long until I made a similar experience when I was working on my doctoral thesis, but this time with respect to a model that is commonly used in text books about flight dynamics.
