Hannover, Universiẗat, Diss., 1998.

Wuppertal, Universiẗat, Diss., 2000.

The prediction of turbogenerator behaviour following fault or disturbance conditions has attracted much interest over the past decade, due to the large amplitude torsional oscillations which can be induced. Many simulation studies have been conducted, but the majority have used d-q models to simulate the electrical machines, and have modelled the turbine shaft damping as constant viscous damping. The d-q machine representation is adequate for balanced conditions, whereas the phase coordinate electrical machine model may be used to simulate unbalanced operation. The latter is adopted for the present work. Constant viscous shaft damping is known to be an over simplification which does not truly reflect the stress level dependent, frequency independent nature of shaft material damping. Although small, the mechanical damping can have a decisive influence over the rate of decay of torsional oscillations, and hence on shaft fatigue life expenditure. This project seeks principally to enhance the shaft torsional model formulation by developing methods of simulating variable shaft damping. Two methods are proposed; one in which a stress-strain hysteresis loop is simulated for each shaft section leading to a variable shaft stiffness, and a second simpler method, in which the viscous damping representation is retained, but with variable viscous damping coefficients. It is shown that the effect of incorporating variable damping is to increase the rate of decay of the initial post-fault oscillations, but then to prolong the subsequent oscillations. This is the effect generally observed in practice on full size turbogenerators. Experimental results from a small single shaft rig also show this effect and agree closely with the predictions of the theory. A brief study of the fatigue life expenditure in a turbogenerator shaft during post-fault oscillations is also presented. It is concluded that both the proposed methods of simulating variable mechanical damping have feasible practical applications, and that the use of variable damping in simulation models can significantly improve the prediction of rate of decay of turbogenerator post-fault torsional oscillations.

Universiẗat, Diss., 2001--Dortmund.

University, Diss.--Karlsruhe, 2005.

Zugl.: Dresden, Techn. Univ., Diss., 2006

Zugl.: Dresden, Techn. Univ., Diss., 2009

The Blended-Wing-Body is a conceptual aircraft design with rear-mounted, over wing engines. Turboelectric distributed propulsion system with boundary layer ingestion has been considered for this aircraft. It uses electricity to transmit power from the core turbine to the fans, therefore dramatically increases bypass ratio to reduce fuel consumption and noise. This dissertation presents methods on designing the TeDP system, evaluating effects of boundary layer ingestion, modelling engine performances, and estimating weights of the electric components. The method is first applied to model a turboshaft-driven TeDP system, which produces thrust only by the propulsors array. Results show that by distributing an array of propulsors that ingest a relatively large mass flow directly produces an 8% fuel burn saving relative to the commercial N+2 aircraft (such as the SAX-40 airplane). Ingesting boundary layer achieves a 7-8% fuel saving with a well-designed intake duct and the improved inlet flow control technologies. However, the value is sensitive to the duct losses and fan inlet distortion. Poor inlet performance can offset or even overwhelm this potential advantage. The total weight of the electric system would be around 5,000-7,000 kg. The large mass penalties further diminish benefits of the superconducting distributed propulsion system. The method is then applied to model a turbofan-driven TeDP system, which produces thrust by both the propulsors array and the core-engines. Results show that splitting the thrust between propulsors and core-engines could have a beneficial effect in fuel savings, when installation effects are neglected. The optimised thrust splitting ratio is between 60-90%, the final value depends on the propulsor intake pressure losses and the TeDP system bypass ratio. Moreover, splitting the thrust can reduce the weight of the electric system with the penalty of the increased core-engine weight. In short, if the power density of the superconducting system were high enough, turboshaft-driven TeDP would be preferable to power the N3-X aircraft.

The Blended-Wing-Body is a conceptual aircraft design with rear-mounted, over wing engines. Turboelectric distributed propulsion system with boundary layer ingestion has been considered for this aircraft. It uses electricity to transmit power from the core turbine to the fans, therefore dramatically increases bypass ratio to reduce fuel consumption and noise. This dissertation presents methods on designing the TeDP system, evaluating effects of boundary layer ingestion, modelling engine performances, and estimating weights of the electric components. The method is first applied to model a turboshaft-driven TeDP system, which produces thrust only by the propulsors array. Results show that by distributing an array of propulsors that ingest a relatively large mass flow directly produces an 8% fuel burn saving relative to the commercial N+2 aircraft (such as the SAX-40 airplane). Ingesting boundary layer achieves a 7-8% fuel saving with a well-designed intake duct and the improved inlet flow control technologies. However, the value is sensitive to the duct losses and fan inlet distortion. Poor inlet performance can offset or even overwhelm this potential advantage. The total weight of the electric system would be around 5,000-7,000 kg. The large mass penalties further diminish benefits of the superconducting distributed propulsion system. The method is then applied to model a turbofan-driven TeDP system, which produces thrust by both the propulsors array and the core-engines. Results show that splitting the thrust between propulsors and core-engines could have a beneficial effect in fuel savings, when installation effects are neglected. The optimised thrust splitting ratio is between 60-90%, the final value depends on the propulsor intake pressure losses and the TeDP system bypass ratio. Moreover, splitting the thrust can reduce the weight of the electric system with the penalty of the increased core-engine weight. In short, if the power density of the superconducting system were high enough, turboshaft-driven TeDP would be preferable to power the N3-X aircraft

Techn. Universiẗat, Diss.--Dresden, 2007.