Development and application of a novel semi-active piezoelectric tuned mass damper for robust vibration control of flexible structures with focus on airframe structures
Loading...
Date
2024-06-17
Authors
Χατζηαθανασίου, Γρηγόριος
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Mechanical systems and structures may experience conditions or dynamic excitations that result in oscillatory motion and vibrations. Flexible structures, such lightweight means of transportations (aircrafts, rotorcrafts, yachts, etc.) are more susceptible to high amplitude vibrations due to their low-frequency and lightly damped structural modes. Vibrations in such structures are attributed to a variety of stimuli, such as motors, rotors, and aerodynamic loads, creating potentially frequency-varying broadband and / or tonal excitations. Contemporary trends towards higher efficiency transport engines and lower weight of the structures (for less fuel consumption and CO2 emissions) using composite materials, lead to higher structural oscillations with lower damping capacity. Excessive vibrations in such structures are undesirable, as they affect the safety and comfort of the passengers, reduce the material fatigue life, and may even lead to structural failure. Therefore, vibration control is extremely crucial in these structures, aiming at the reduction of the amplitude of the vibrations, in order to ensure the reliability of their function. An appropriate antivibration mechanism should exhibit multi-modal and multi-tonal vibration control capabilities, adaptability to potentially frequency-varying applied loads, and minimal requirements for added weight and power supply.
Towards the vibration control of flexible structures that satisfy these demanding requirements, this dissertation addresses the development and application of a novel semi-active electromechanical antivibration device, comprising an auxiliary mass, mounted on a specialty piezoelectric device, whose terminals are connected to a shunt resistive-inductive (RL) circuit. The piezoelectric device provides the stiffness for the resonant mass oscillator and introduces high electromechanical energy conversion and coupling. This concept is very promising in terms of high and versatile vibration attenuation potential, due to its various mechanisms for absorbing and dissipating the host structure kinetic energy. The transformed, by the piezoelectric device, electrical energy can be dissipated into heat, due to the shunt circuit tunable resistance, while the resonant mass and the inductance-tunable shunt circuit eigenfrequency can absorb very high vibrational energy (energy sinks). The proposed device combines the high vibration control capabilities of the tuned mass damper (TMD) and the great tuning and controlled damping characteristics of the shunt piezoelectric device. Therefore, this device is defined in this dissertation as a piezoelectric semi-active tuned mass damper (SATMD).
Initially, a specialty piezoelectric transducer is carefully selected to exhibit low effective stiffness and high piezoelectric coefficient. The rest components of the SATMD antivibration device are designed and assembled on the selected piezoelectric transducer. The sole SATMD is modeled and experimentally characterized, revealing two pairs of electromechanically coupled poles. The experimentally demonstrated effects of the shunt circuit impedance are compared to computational results, showing great agreement.
Next, the performance of the piezoelectric SATMD is evaluated experimentally and numerically on a simplified lumped mass structure. The dynamic equations of motion of the SATMD – host structure system are formulated. The transfer functions show that the introduced antiresonances on the host structure coincide with the sole SATMD eigenfrequencies. Resistance increases the damping capabilities of the coupled electromechanical system, while inductance introduces a new, highly tunable, oscillator in the system, which enhances the coupling and conversion of kinetic to electrical energy. The SATMD can compensate for the purely mechanical TMD disadvantages, providing broadband vibration suppression, and offering great retuning capabilities. The experimental measurements validate the developed models.
The performance of the antivibration device capabilities is subsequently presented on large and flexible structures. For the computational model, a reduced-ordered modal space structural dynamics model is formulated, coupled with the SATMD device, and the RL shunt electric circuit. The SATMD is attached to a scaled-down airframe prototype, which is used as the laboratory testing structure. The SATMD demonstrates great multi-modal and multi-tonal vibration attenuation capabilities. Furthermore, it is shown that the two introduced antiresonances are independent of the host structure dynamic characteristics, and as a result the appropriate SATMD auxiliary mass and inductance can be decided based only on the structure frequency response. This special and versatile feature is used for the antivibration performance of the SATMD on a BO105 S helicopter, accomplishing beneficial reduction to two excessive vibration frequencies during real-flight conditions.
Furthermore, the SATMD design strategy is studied, aiming at multi-modal vibration reduction of the scaled down-airframe model, under broadband excitation. The optimal parameters are compared to an ad-hoc design strategy. Including the auxiliary mass in the optimization scheme, simultaneous 90% acceleration reduction is achieved in all studied structural modes, and it is proved that the auxiliary mass is not necessarily optimally tuned to a host structure mode.
Finally, an adaptive control concept and algorithm is developed based on the effects that each of the tunable parameters (resistance and inductance) introduces to the host structure behavior. Estimates of the frequency response of the structure are based on the measured acceleration, yielding the highest frequency peak (critical frequency) at each control time period. The inductance to suppress each critical frequency is independent of the host structure dynamics, whereas the resistance is calculated based on the acceleration response of the structure. The developed adaptive algorithm is tested on the scaled-down airframe model, which is assumed to undergo both gradual and abrupt mass alterations. The adaptive SATMD achieves great continuous vibration control, proving the effectiveness of the developed algorithm.
Description
Keywords
Structural dynamics, Flexible structures, Semi-active vibration control, Tuned mass damper, Piezoelectric materials, Electrical shunt circuit