Institute of Fundamental Technological Research

An experimental and modelling study of the properties of a prototype layered beam with a core made of a non-Newtonian sand mixture is presented. The non-typical dilatant sand was covered with an elastic envelope that restricted its movement, which allowed us to pressurise the grains by evacuating the air from within the cover. By applying controlled underpressure, the compressed sand grains become jammed, which resulted in an increased stiffness and damping. This gives the possibility to attenuate vibrations of a cantilever in an adaptive manner. The experiment was performed for free vibrations and prescribed sinusoidal base motion, to demonstrate the possibility of tuning material parameters in a vast range. The experimental amplitude, frequency and damping capacity of the kinetic sand are discussed. An analytical model is proposed to verify how many parameters are necessary to describe the material behaviour. Based on the experimental results, a parameter identification of a custom rheological model is performed and practical simplifications reducing complexity of the problem are elaborated. The performed parameter identification is indispensable for the further development of potential control strategies for effective vibration abatement of dynamic systems using such types of alternative smart materials.

Granular material,Damping,Dilatant sand,Identification,Control

A container partially filled with loose plastic granules was attached to the shovel of the snowboard to suppress large-amplitude lateral vibrations by dissipating energy through non-conservative multi-granule interactions. A custom laboratory stand allowed to evaluate the performance using a full-scale snowboard deck. The response of the system with a prototype granular dissipator was measured for free lateral vibrations of the initially deflected board and under prescribed sinusoidal base motion. The damping characteristics for different fill ratios of the container were obtained using a direct method of nonparametric identification. The applied Hilbert–Huang transform-based vibration analysis method gave more insight into the board’s damping performance than the logarithmic decrement analysis. The results show that using the granular dissipator with a predestined number of granules increases the damping capacity at large amplitudes but is less effective at small amplitudes. At best, the damping factor was 70% higher when the granular dissipator was used than when the board was damped only intrinsically.

Vibration, Damping, Granular material, Dissipation, Hilbert transform, Bending

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.

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

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.

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