Vicoter, in cooperation with Lord-Parker Corporation and the Department of Aerospace Sciences and Technologies of the Politecnico di Milano, is carrying out a research related to passive vibration suppression. The activity is funded by the European Community as part of the Clean Sky 2 research project called ‘EMS-UHPE – Engine Mount System for Ultra High Pass Engine’. Specifically, it is aimed at identifying and testing an innovative vibration abatement technologies to be used in the aeronautical environment, in particular in the engine field, capable of reducing the impact of resonances on the design limits, allowing a lightening of the components.
To date, one of the best solutions has been the Particle Impact Damper (PID). This technology involves the use of a certain number of particles (spheres, but also particles of other shape), placed inside a casing connected to the structure to be damped, capable of transforming the kinetic energy into heat by collisions among the particles and between the spheres and the casing walls.
The PID is capable to obtain high damping in a wide band of frequencies, with a considerable manufacturing freedom and the possibility of being used even in hostile environments (e.g. high temperature), without being affected by aging effects, unlike other classic solutions like treatments based on viscoelastic materials. Despite this great flexibility of use, PID presents a strongly non-linear behavior which makes it difficult an optimal design, due to the presence of many design parameters.
Vicoter and the Politecnico di Milano are carrying out an experimental campaign with an integrated simulation / experimentation approach, aiming at identifying the sensitivity of the introduced damping with respect to several quantities, such as the amount of acceleration on the structure, the type of excitation (sinusoidal, random, …), the frequency of work, the number and the material of the spheres, the dimensions of the casing, the positioning of the apparatus, the sensitivity to transverse accelerations.
A simple but significant experimental apparatus has been prepared. A thin aluminum plate, stuck at one end, is used as test structure. Its first three flexural modes (up to about 150 Hz) are excited by an electrodynamic shaker. The introduced force is measured through a load cell, while three accelerometers are used to detect acceleration in some points of the beam and two laser sensors are used to measure both the vertical displacement and, through a finite spatial difference, the device rotation.
For the purposes of normalizing the results and of keeping the sphere movement as constant as possible, the tests are performed by imposing a constant average vertical acceleration, independent of the frequency, at the free end of the beam.
The results obtained to date confirm that, if correctly designed, a PID is able to achieve appreciable reductions in the resonance peak (up to 20 times) with a limited increase in weight and a reduced impact on the host structure.
However, since the mass of the particles is one of the most important factors driving the dispersion of energy, the trade-off between the PID performance and the weight burden for real structures is still under study.