# Damping of Beam Vibrations Using Tuned Particles Impact Damper
## 6 Conclusions  
The novelty of the proposed TPID device is the application of a special balloon, that has variable volume and is filled with granules. Through inflating and deflating the previously mentioned balloon, the TPID device volume is shifted in a controlled manner, enabling the rapid change of its damping parameters--the volume ratio of particles and container. Damping properties of granules made of plastic, steel and their combinations have been experimentally tested. In addition, tests were carried out for various cases of the container filling ratio and grains mass for the full range of excitation frequencies (before, in resonance and after resonance ranges). Experiments confirmed that the proposed TPID damper structure retains the advantages of standard PID devices ([3; 5; 7; 22]). It was also observed that the type of grains material strongly affects the damping properties of the granular damper. The particles are characterized by various physical parameters, for example, Young's modulus. Differences in values of the particles restitution coefficient cause changes in the grains movement and collisions character. They also result in different values of contact forces. Basing on detailed analyses of experimental data the authors concluded that the plastic particles allow for a wide range of controllability and tuning of the system response. Another parameter that significantly influences the dissipative properties of investigated TPID prototype is the mass of the particles. Laboratory tests revealed that increasing the mass of granular material being involved in inelastic collisions inside the PID container improved the damping features of the prototype. Obviously some specific threshold value for the number of particles being involved in the damping process exist. Exceeding this value will cause the limitations of free space for intergranular impacts and consequently will lead to decreasing the dissipative properties of the system. This complex phenomenon, dependent not only on the filling ratio of the TPID, but also on the shape of grains and container and materials involved in contacts, was not discussed in the paper. Assuming too low a mass of granular materials (insufficient number of particles) will not provide the desired vibrations attenuation effect. The authors assumed that the Young's modulus is the main parameter of granular material that affects the damping properties. Defining in an empirical way the energy dissipation components is a challenging task. At the current stage of investigations the authors did not conducted such tests. The shape and changeable in time volume of the container make the described problem more complicated. The TPID container was developed by the 3D printing technique. The applied filament material is much softer than the grains material. The problem of investigating the container's material influence on the global damping properties of the system (TPID effectiveness) is important and requires carrying out additional and time-consuming studies. Also crucial from the operational point of view effects of grains degradation or temperature changes were not discussed in the paper. The biggest advantage of the proposed TPID prototype is the possibility of adjusting its damping characteristics according to various types of temporary excitations. Discussed proposition by simply adding the expandable balloon to the classical PID device enabled the user to fully control the volume of the grains casing (by the external pump) and in fact transformed the passive PID device into the innovative semi-active TPID damper. In the modeling section the simple 2 DOF linear mathematical model was adopted. To capture nonlinearities of the real system resulted from the inelastic character of collisions inside the granular media the exponential activation function was proposed. The function confirmed its reliability not only for the \"on\" and \"off\" states of the TPID but also allowed us to achieve satisfactory results for various transient states of the device being inflated.