doc. Ing. Martin Hromčík, Ph.D.

Flutter is a dynamic instability of an elastic structure - an aircraft - in a fluid flow, caused by positive feedback between the body's deflection and the force exerted by the fluid flow. In a linear system, 'flutter point' is the point at which the structure is undergoing simple harmonic motion - zero net damping - and so any further decrease in net damping will result in a self-oscillation and eventual failure. Prevention of aircraft flutter is done traditionally by mechanical modifications - by changing mechanical stiffness and/or mass distribution essentially. The weight penalty is essentially inevitable in this case however. For this reason, active control approaches have been considered in recent years, and in a very limited number of cases, they have got to final implementations. In all cases however, the solutions aimed at large transportation or military projects. The main goal of this project though is to develop solutions applicable for small transportation aircraft: either of the GA category, or "ultralights" (small sports aircraft) where the flutter issue is critical. The specifics for these categories are related to technical limitations in instrumentation and to legal and certification issues (often fully mechanical instrumentation is expected or requested). Flutter led to many documented catastrophic causalties of ultalight aircraft in the Czech Republic in the past. Expected technical outputs are simulation flight mechanics models for selected case studies, designed control laws, simulation validation and verification, realization of an experimental setup, and experimental tests in wind tunnel. Collaboration on experimental validation of results is planned with the Aerospace Department, FME CVUT, which also serves as an accreditted lab for flutter cerrtificates of ultralight aircraft.

The goal is to develop and validate - by simulations and HIL testing - control algorithms which take full advantage of the near-future electric cars, and to solve selected particular electric drivetrain outstanding problems. Existing concepts applied today in electronic stabilization systems and related assitive systems for conventional cars (ABS, ESR, active differentials) shall be developed to a new level by considering independent wheels drive (torque vectoring), reccuperative braking, battery management considerations. Advanced model-based optimal and robust control design approaches (constrained optimization, fixed order controllers, polynomial and piecewise affine LPV systems and control, nonlinear MPC, direct adaptive control) shall be investigated. Further, reported drivetrain-vibration problems shall be studied and treated using the concepts of input shaping, active damping, and active resonators.

Current interest into electrically powered aircraft of all types presents new possibilities and challenges for the control systems design. The usage of electric propulsion seems to lead to distributed and over-actuated system with new capabilities, such as VTOL, STOL or thrust vectoring, that has not been seen in civil aviation. The usage of distributed propulsion has also increased the importance for dynamic instability of elastic aircraft structure, that cannot be prevented with mechanical modifications, as the weight increase would be significant and unavoidable. The main goal of this project is to develop and validate, through simulations and subscale model testing, control algorithms, that take full advantage of distributed electric propulsion in order to increase flight efficiency or enable new VTOL, STOL capabilities. The developed algorithms should take into consideration the airframe flexibility in order to reduce the stiffness requirements for the mechanical structure. Expected technical outputs are simulation flight mechanics models for selected case studies, designed control laws, simulation validation and verification, realization of an experimental setup, and experimental tests in wind tunnel.

The project focuses on the application of semidefinite programming for solving numerically nonconvex optimal control problems with polynomial data, with a special focus on problems coming from aerospace systems control. The goal is to develop validation and verification framework for spacecraft with significant flexibility in their mechanical construction, for which the guarantees of often extreme required accuracies in orientation are difficult or impossible to get, by the nowadays common massive high-fidelity simulation campaigns, capturing all nuances of parameter uncertainties and combined with effects of external disturbances. The project aims to build on experience gained in a previous successful PhD project focused on flexible aircraft adaptive control. The technical partner, and partial sponsor of this PhD position, is the VZLU research institute in Prague, with their satellite programme.