## 5 Results and Discussions
It has been observed that the empty HCDP (gray dashed line) either increases the vibration amplitude or shows no damping effect, except for the resonance peak near 150 Hz, where the damping value due to empty HCDP is similar to the damping value obtained by attaching a SU HCDP filled with rubber powder with filling ratio FR1 (orange dashed line). Nevertheless, attaching empty HCDP between the stator arm and ring increase the overall vibration amplitude of the primary structure, which can be observed in the SL value of the surface velocity, see Figure 8.5 Although, mounting the SU or MU HCDP between the stator arm and ring can reduce the vibration amplitude. However, for the real-world application, this configuration can be very critical as it can make the complete WTS structure unstable. Currently, at an industrial scale welding process is used to join the WTS arm and ring together. Attaching the partially filled HCDP at this particular location in the WTS will require an extensive analysis of the fastening joining process. Hence, implementation of the above mentioned configuration at an industrial scale is tedious for the manufacturing, production, and assembling process. In the next step, SU HCDP is mounted to the inner wall of the WTS ring (on the excitation point side), see Figure 8.6 The results of this configuration can be seen in Figures 17-18. As expected, this configuration also exhibits a similar number of resonance frequencies as discussed for others locations of HCDP. It has been observed here that mounting partially filled HCDP at this location can reduce the vibration amplitude significantly for the resonance peaks near 50 Hz, 100 Hz, and 355 Hz, see Figure 8.7 However, vibration attenuation due to granular materials is not observable because the reduction in vibration amplitude due to the empty HCDP is very similar to the partially filled HCDP. This observation can also be justified by comparing the SL values of surface velocity. Furthermore, the filling ratio also shows almost no influence on damping. Hence, it can be concluded that mounting HCDP at this location may increase the bending stiffness of the primary structure, which is mainly responsible for the vibration attenuation, i.e., reduction in vibration amplitude, which can be seen in Figures 17-18, is because of higher bending stiffness and not due to particle damping mechanism. This observation is reasonable as the width contributes linearly to both the resulting stiffness and mass. In a follow up, SU and MU HCDP are mounted at different locations to WTS test specimen simultaneously, namely: configuration 1, configuration 2, and configuration 3. In configuration 1, a MU HCDP filled with stone powder and sand is mounted to the outer wall of the WTS ring because as discussed above, this combination of HCDP yields maximum vibration attenuation of the WTS test specimen. Along with this, a SU HCDP filled with tungsten powder is attached between the stator arm and ring because at this location tungsten powder shows broadband damping, see Figure 8.8 This configuration reduces the vibration amplitude by 1.4 dB, 10.4 dB, and 15.0 dB at resonance peaks near 50 Hz, 150 Hz, and 355 Hz, respectively, see Figure 8.9 The setup for configuration 2 is very similar to configuration 1, in which only SU HCDP is attached to the WTS test specimen, see Figure 9.0 This configuration is only effective for resonance peaks near 150 Hz and 355 Hz, see Figure 9.1 Configuration 3 is an extension of configuration 1, in which an empty HCDP is attached to the inner wall of the WTS ring at the excitation point side. The decision for attaching an empty HCDP at this position was taken because at this location damping is coming due to higher bending stiffness of the primary structure and not because of granular materials. The damping characteristic of this configuration is very similar to the damping characteristic of configuration 1. The SL values of all three configurations mentioned above are almost similar and are larger than the reference specimen SL values (158.28 dB).