Methods and tools for aeroservoelasticity and active structural control, with applications

Research focus

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The research activities developed during the last years at DIA cover the most challenging topics generally grouped under the common umbrella of the so-called modern aeroservoelasticity, which includes: reduced state-space models and their interface with actuators and controllers, development of methods and tools for flutter analysis and gust load response, CFD-based aeroelasticity of fixed and rotary-wing vehicles, aeroelasticity of wind turbines, design and testing of active control systems for aeroelastic control and vibration suppression. CFD-based aeroelasticity represents today one of the most interesting fields of research for fixed-wing aircraft. During the last 5 years, DIA implemented a complete procedure for CFD-based aeroelastic analysis showing the following capabilities: partitioned Fluid-Structure Interaction (FSI), use of off-the-shelf industrial codes for CFD and Structural models (specifically, FLUENT and NASTRAN), meshless approaches for conservative aerodynamic-structural coupling, linearised unsteady aerodynamic Reduced Order Models obtained by small perturbations with assigned time-histories, definition of robust and efficient grid motion algorithms based on a continuum analogy. The procedures have been validated for trainers as well as regional transport aircrafts. In the field of aeroelasticity of rotary wing vehicles, the tools developed at DIA are based on the integration of multibody codes for structural and aeromechanical models with ad hoc in-house developed aerodynamic models. The research in this area has strong synergies with the activities more fully described in Research Topics 2.2.2.1 and 2.2.2.3. The work has lead to significant collaborations with AgustaWestland and with foreign research entities. The expertise of the research unit in the area of rotorcraft vehicles has been recently applied to the field of wind turbine aeroelasticity and active control. Specifically, work has been focused on the development, validation and integration in an industrial environment of general purpose multibody-based simulation tools for the aeroservoelastic modeling of wind turbines, implementing all necessary wind models and procedures of the IEC (International Electrotechnical Commission) standards. Under a close collaborative effort with industry, the new procedures have been validated with respect to industrial standards and experimental data. In the active control area, work has been directed towards model-based pitch-torque predictive and adaptive control algorithms, capable of automatically adjusting to varying environmental and operative conditions. To support this activity, novel state observers have been developed based on Kalman-type techniques, including wind observers which do not rely on imprecise readings from the on-board anemometers. This control technology, implemented in-house on small-form-factor single-board computers, is currently being tested by industry on instrumented wind turbine prototypes in the field. The active control of vibrations is a key research field especially for what concerns helicopters. In fact, the need of increasing cabin comfort levels has determined great interest on active vibration control techniques, in order to minimize the vibrations transmitted by the main rotor to the cabin. During the last years DIA has devoted a significant effort to this research field, in the framework of EU funded research projects and in close cooperation with the helicopter industry. The numerical activity was developed in parallel with the experimental one, whose main experimental asset is a full scale helicopter hosted in the DIA main lab. The active control techniques developed in this area are based on the use of piezo-patches located on the elements linking the main rotor/gear-box group to the cabin structure; the attention is mainly focused on the reduction of high frequency tonal vibration/noise produced by the helicopter gearbox meshing, the most annoying from the psycho-acoustic point of view. Significant results have been achieved for tones up to 4200 Hz, a control bandwidth which has been enabled by the use of a high performance real-time environment (RTAI), operating at frequencies above 14kHz and with the use of very complex control laws. The need to test active control systems for aeroelastic control and vibration suppression stimulated DIA to develop an ‘in-house’ real-time environment for the design and testing of control laws in a cost-effective and efficient way. To this aim, the RTAI project was started at DIA in 1996, to develop a flexible, efficient and non-commercial code for the implementation of advanced digital controllers for generic aeroservoelastic systems. RTAI is integrated into the Linux operating system to handle real time applications. For efficiency, the software allows for the separation of real time applications and processes without temporal constraints; this way, the same PC can be used for the implementation of the controller and its supervision. Furthermore, the software supports the implementation of complex distributed control systems, while a specific tool, RTAILab, allows for the interfacing to high level prototyping packages, like MATLAB-Simulink and SCILAB/Scicos.

Dipartimento di afferenza

Dipartimento di Ingegneria Aerospaziale

Docenti afferenti

Gian Luca Ghiringhelli (Full Professor)
Massimiliano Lanz (Full Professor)
Paolo Mantegazza (Full Professor)
Carlo Luigi Bottasso (Associate Professor)
Sergio Ricci (Associate Professor)
Giampiero Bindolino (Assistant Professor)
Lorenzo Dozio (Assistant Professor)
Pierangelo Masarati (Assistant Professor)
Lorenzo Trainelli (Assistant Professor)