Open Access

Foil-air bearings (FABs) are predominantly used for high-speed, oil-free applications. Offering many advantages such as friction loss at high speeds, stability and price, they lack, however, load capacity as well as start-up and coast-down friction wear resistance. The friction losses of FABs have been studied experimentally by many authors. In order to predict the friction and, consequently, the lifespan of a FAB, the start-up and coast-down regimes are modelled in such a way that allows for accurate, efficient simulation and later optimisation of lift-off speed and wear characteristics. The proposed simulation method applies the Kirchhoff-Love plate theory to the top foil mapping [20]. This system of differential equations is coupled with the underlying compliant foil to simulate the displacement due to the pressure buildup. Consequently, this coupled system allows for simulation from almost zero rounds per minute (rpm) to full speed. The underlying simulation model uses the finite difference method for spatial discretisation and a temporal explicit Runge-Kutta method. Difficulties to overcome are the smooth combination of various friction regimes across the sliding surfaces as well as the synchronous coupling of Reynolds, deformation and kinematic equations with highly non-linear terms. Introducing an exponential pressure component based on Greenwood and Tripp’s theory avoids impingement between the rotor and foil.

Das Ziel dieser Arbeit war die Konzeption eines untergeordneten Stadtbusnetzes der Stadt Konstanz. Dabei wurde auf einem bereits entwickelten Entwurf eines übergeordneten Netzes aufgesetzt. Durch die Kombination dieser beiden entstand ein Gesamtbusnetz. Im ersten Schritt wurde eine breit gefächerte Bestandsanalyse durchgeführt, inbegriffen war dabei eine Analyse des übergeordneten Busnetzes. Die gebündelten Ergebnisse gaben den Rahmen für die Konzeption vor. Danach folgte der schrittweise Entwurf der einzelnen Linien des untergeordneten Netzes. Im letzten Schritt der Konzeption wurden die Linien an wichtigen Umsteigeknoten und Parkräumen aufeinander abgestimmt. Aus der genannten Analyse resultierten diverse Anforderungen für die Konzeption eines neuen Busnetzes. Hierbei konnte die Anbindung an die Bahn und das neu entstehende Mobilitätszentrum besonders hervorgehoben werden. Das Ergebnis der Konzeption waren elf Buslinien, die dem untergeordneten Netz zugewiesen werden können. Gemeinsam mit den fünf Linien des übergeordneten Entwurfs bilden sie ein Gesamtstadtbusnetz. Dabei wurden die Streckenverläufe der Linien aufeinander abgestimmt, sodass ein breitgefächertes Netz an Direktverbindungen entstehen konnte. Mithilfe der Abstimmung an Umsteigeknoten konnten sinnvolle Umsteigerelationen geschaffen werden, wodurch die Direktverbindungen zu einer flächendeckenden Anbindung der Stadtteile an relevante Ziele im Stadtgebiet erweitert wurden. Auf theoretischer Ebene wurde hier aufgezeigt, wie ein neues Buskonzept der Stadt Konstanz gestaltet sein kann. Das vorliegende Konzept sollte in einer separaten Arbeit auf eine tatsächliche Umsetzbarkeit geprüft werden.

This thesis deals with the object tracking problem of multiple extended objects. For instance, this tracking problem occurs when a car with sensors drives on the road and detects multiple other cars in front of it. When the setup between the senor and the other cars is in a such way that multiple measurements are created by each single car, the cars are called extended objects. This can occur in real world scenarios, mainly with the use of high resolution sensors in near field applications. Such a near field scenario leads a single object to occupy several resolution cells of the sensor so that multiple measurements are generated per scan. The measurements are additionally superimposed by the sensor’s noise. Beside the object generated measurements, there occur false alarms, which are not caused by any object and sometimes in a sensor scan, single objects could be missed so that they not generate any measurements. To handle these scenarios, object tracking filters are needed to process the sensor measurements in order to obtain a stable and accurate estimate of the objects in each sensor scan. In this thesis, the scope is to implement such a tracking filter that handles the extended objects, i.e. the filter estimates their positions and extents. In context of this, the topic of measurement partitioning occurs, which is a pre-processing of the measurement data. With the use of partitioning, the measurements that are likely generated by one object are put into one cluster, also called cell. Then, the obtained cells are processed by the tracking filter for the estimation process. The partitioning of measurement data is a crucial part for the performance of tracking filter because insufficient partitioning leads to bad tracking performance, i.e. inaccurate object estimates. In this thesis, a Gaussian inverse Wishart Probability Hypothesis Density (GIW-PHD) filter was implemented to handle the multiple extended object tracking problem. Within this filter framework, the number of objects are modelled as Random Finite Sets (RFSs) and the objects’ extent as random matrices (RM). The partitioning methods that are used to cluster the measurement data are existing ones as well as a new approach that is based on likelihood sampling methods. The applied classical heuristic methods are Distance Partitioning (DP) and Sub-Partitioning (SP), whereas the proposed likelihood-based approach is called Stochastic Partitioning (StP). The latter was developed in this thesis based on the Stochastic Optimisation approach by Granström et al. An implementation, including the StP method and its integration into the filter framework, is provided within this thesis. The implementations, using the different partitioning methods, were tested on simulated random multi-object scenarios and in a fixed parallel tracking scenario using Monte Carlo methods. Further, a runtime analysis was done to provide an insight into the computational effort using the different partitioning methods. It emphasized, that the StP method outperforms the classical partitioning methods in scenarios, where the objects move spatially close. The filter using StP performs more stable and with more accurate estimates. However, this advantage is associated with a higher computational effort compared to the classical heuristic partitioning methods.

The intentions of the so-called "More Electrical Aircraft" (MEA) are higher efficiency and lower weight. A main topic here is the application of electrical instead of hydraulical, pneumatical and mechanical systems. The necessary power electronic devices have intermediate DC-links, which are typically supplied by a three-phase system with active B6 and passive B12 rectifiers. A possible alternative is the B6 diode bridge in combination with an active power filter (APF). Due to the parallel arrangement, the APF offers a higher power density and is able to compensate for harmonics from several devices. The use of the diode bridge rectifier alone is not permitted due to the highly distorted phase current. The following investigations are dealing with the development of an active power filter for a three-phase supply with variable frequency from 360 to 800 Hz. All relevant components such as inductors, EMC-filters, power modules and DC-link capacitor are designed. A particular focus is put on the customized power module with SiC-MOSFETs and SiC-diodes, which is characterized electrically and thermally. The maximum supply frequency slope has a value of 50 Hz/ms, which requires a high dynamic and robustness on the control algorithm. Furthermore, the content of 5th and 7th harmonics must be reduced to less than 2 %, which demands a high accuracy. To cope with both requirements, a two-stage filter algorithm is developed and implemented in two independent signal processors. Simulations and laboratory experiments confirm the performance and robustness of the control algorithm. This work comprehensively presents the design of aerospace rectifiers. The results were published in conferences and patents.

Hongkong steht als Welthandelsmetropole auch für Superlative des Bauens. Dies gilt für die in britischer Zeit errichteten Bauten, aber auch für die nach der Übergabe an China entstandenen Hochhäuser und Brückenbauwerke. Der Exkursionsbericht der Fakultät Bauingenieurwesen der HTWG Konstanz gibt einen Eindruck von diesen Aktivitäten. Er schildert Brücken- und Hochhausbauten, Tunnelbaustellen und die Baustelle eines Klärschlammverbrennungswerks, die während einer Exkursionswoche im September 2012 besichtigt wurden. Darüber hinaus gibt er einen Einblick in die wirtschaftliche Dynamik der Stadt.