Fall 2025
Wednesday, December 17, 2025
10:00 am | Clark 205
Student: Lancert Foster
Advisor: Peter Thomas
Title: Dynamic Control of Turbine-Based Combined Cycle Inlet Mode Transition
Abstract: Turbine-Based Combined Cycle (TBCC) propulsion is a concept for reusable hypersonic flight. A TBCC propulsion system consists of a turbine engine to pro-pel the vehicle at takeoff, and a ramjet or scramjet to take over at higher speeds. The handoff from turbine to ramjet engine is known as mode transition and is a key enabling technology for TBCC vehicles. This thesis investigates TBCC mode transition as an optimal control problem and seeks to develop control laws for the splitter, a device that controls airflow distribution between the two engines.
TBCC mode transition is a problem at the juncture between aircraft GNC (Guid- ance, Navigation, and Control) and propulsion control. Consequently, there is no established classical framework for the problem. A change of variables was performed on a classical aircraft GNC state space description, to produce a propulsioncentric viewpoint of the vehicle trajectory dynamics. The dynamic system characterization developed in this thesis presents a novel state space framework, not seen in the known literature. This framework shows a clear path for trajectory optimization, as well as linearization for control design modeling. Engine performance models were generated from standard compressible flow relations. Trajectory simulations were performed, modeling a vehicle in TBCC mode transition. A standard set point controller was employed for splitter sequencing, with simulations including multiple splitter speeds and transition Mach numbers. As expected, a faster splitter transition was helpful in crossing the thrust gap and achieving successful mode transition. Nonetheless, trajectories with slower splitter motion showed greater initial acceleration. Fortuitously, optimal splitter sequencing for TBCC mode transition requires second-order time variation consistent with the motion of real actuator devices.
Fall 2025
Thursday, December 4, 2025
4:00 pm | Rockefeller 304
Student: Yinhui Liu
Advisor: Peter Thomas
Title: On the Effects of Molecular Fluctuations on Digital Logic Circuits Engineered from Genetic Regulatory Systems
Abstract: Recent efforts in synthetic biology have implemented elements of digital logic circuits such as logical negation, logical NOR, and set-reset latch in genetic circuits in genetically engineered bacteria. In this thesis, we consider the effects of molecular fluctuations arising from small copy numbers of the DNA, RNA, and proteins constituting these circuits. We use stochastic simulation methods to investigate the behavior of model systems representing logical negation, logical NOR, and set-reset latch. We study the effects of noise on the performance of these systems using a combination of information theory measures and first-passage time distributions. We conclude that it may be important to take stochastic effects into account when designing synthetic genetic circuits.