Institute of Fundamental Technological Research
Polish Academy of Sciences

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Prof. Jerzy Bajkowski, PhD, DSc


Recent publications
1.  Bajkowski J.M., Dyniewicz B., Bajer C.I., Bajkowski J., An experimental study on granular dissipation for the vibration attenuation of skis, Proceedings of the Institution of Mechanical Engineers, ISSN: 1754-338X, DOI: 10.1177/1754337120964015, pp.1-8, 2020

Abstract:
Due to the continuous deformations and irregularities of the surface of snow, alpine skis exhibit dynamic excitation, leading to drastic vibrations and decreased manoeuvrability. Therefore, attenuating these unwanted vibrations, while ensuring that the ski experience is not compromised, is an important challenge. The possibility of using granular material in a damping device is studied in this paper. A container that was partially filled with loose granules was fixed at the tip of an alpine ski to suppress vibrations by dissipating energy through collisions. The performance was verified experimentally by studying the transient response of a ski mounted in a horizontal cantilever orientation. Moreover, on-snow tests were performed. Different numbers of plastic granules were used as a dissipating material. To identify the nonlinear damping characteristics of the system, a Hilbert transform was used. In the laboratory test, the displacement amplitude decay was up to 16 percentage points higher when a granular dissipator was attached to the ski than without the damper. During field testing, acceleration amplitudes were 9% lower compared to the ski without the dissipator. This solution could possibly be adapted to other boardsports on a wide variety of terrain, including ground, water and snow.

Keywords:
vibration damping, alpine ski, granular material, Hilbert transform, bending beam

Affiliations:
Bajkowski J.M. - Warsaw University of Technology (PL)
Dyniewicz B. - IPPT PAN
Bajer C.I. - IPPT PAN
Bajkowski J. - other affiliation
2.  Bajkowski J.M., Dyniewicz B., Gębik-Wrona M., Bajkowski J., Bajer C.I., Reduction of the vibration amplitudes of a harmonically excited sandwich beam with controllable core, MECHANICAL SYSTEMS AND SIGNAL PROCESSING, ISSN: 0888-3270, DOI: 10.1016/j.ymssp.2019.04.024, Vol.129, pp.54-69, 2019

Abstract:
We consider a theoretical analysis and experimental test of a sandwich beam, with a core layer made of controllable material that can change its properties over time. We show that this dynamically excited beam can be sequentially controlled to obtain higher amplitude attenuation and resistance to the amplitude growth in resonant ranges than when the smart beam parameters are constant over time. Numerical simulations were performed to study the possibility of shifting beam vibration frequency towards ranges distant from resonance. An experimental study on a layered beam consisting of two steel bars with a pneumatically controlled core made of pressurized granular material was considered. A simplified control was performed to detune the beam from the resonance frequencies and reduce the vibrations by 30% in simulations and 10% in experiment.

Keywords:
smart material, granular structures, structural control, semi-active control, layered beam

Affiliations:
Bajkowski J.M. - Warsaw University of Technology (PL)
Dyniewicz B. - IPPT PAN
Gębik-Wrona M. - other affiliation
Bajkowski J. - other affiliation
Bajer C.I. - IPPT PAN

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