## 4 Experimental Setup  
The surface velocity of the WTS test specimen is measured by using a laser scanning vibrometer (LSV) of model PSV-400 from Polytec. The LSV works on the Doppler effect principle and is a contactless optical measuring technique. LSV allows the out-of-plane, as well as the in-plane measurement of surface velocity. It is always the vector of velocity, which is measured in the direction of the laser beam. The experimental setup is shown in Figure 4. As mentioned previously, in this contribution the efficiency of particle damping technology is investigated by assembling the partially filled HCDP at different locations of the WTS test specimen. To perform this process, assembling and reassembling of each component of the test specimen is required after each set of experiments. This procedure is time-consuming and can also cause several number of uncertainties that can be problematic for reproducing the experimental results. To overcome this problem, i.e., to secure comparable results in all measurements, a clamped boundary condition is considered here that also resembles the real-world scenario. To realize the clamped boundary condition, two identical beam-like structures of steel are constructed and attached to the bottom surface of the stator ring with four bolts of similar dimensions. Afterwards, \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Filling Material** & **Filling Ratio** & **Filling Material Mass** & **Total Mass of HCDP** \\ \hline Empty & & & 67.0 g \\ Sand & FR1 & 54.2 g & 121.2 g \\  & FR2 & 25.8 g & 92.8 g \\ Stone powder & FR1 & 46.7 g & 113.7 g \\ Rubber powder & FR2 & 22.5 g & 89.5 g \\ Tungsten powder & FR1 & 16.1 g & 83.1 g \\ \hline Tungsten powder & FR2 & 49.9 g & 116.9 g \\ \hline \hline \end{tabular}
\end{table} 
Table 2: List of filling materials, filling ratios (FR2 = 0.5 FR1), filling material mass and total mass of the HCDP. with the help of four identical bolts and sliding blocks the stator ring with an attached beam-like structure is fixed on the measuring table. The stator arm of the test specimen is assembled on the top of the stator ring by using four identical bolts, nuts, and washer arrangement. For the entire experiment, the stator ring is kept fixed and only the stator arm is assembled and disassembled if required. In previous studies [18] and also in the current investigation, it has been observed that the structure vibration behavior is also dependent on the bolt tightening procedure. Therefore, it is necessary to maintain the same preload on all bolts for each configuration. Hence, the bolt tightening procedure is carried out with the help of a torque wrench. For assembling the stator arm 6 Nm torque is applied on each bolt. The location of the excitation point is chosen on the outer side of the stator ring and kept fixed for all the experiments to obtain a comparable frequency spectrum. This location was chosen to approximate the real-world scenario and also to obtain as many as possible eigenmodes below 355 Hz. To excite the test specimens an electrodynamic shaker from TIRA has been used. A certain distance is required to be maintained between the impulse hammer head in the test specimen to avoid the double stroke near the excitation point. To fulfill this requirement, a distance of approximately 2 mm is kept fixed between the stator ring and impulse hammer head. To avoid unintended secondary vibration path from shaker to the WTS test specimen the shaker is mounted on an iron frame throughout the experiment. To keep the excitation point identical for each experimental setup, the stator ring is kept fixed for the entire duration of the experiment. A force sensor of model 208C02 from PCB Piezotronics is mounted between the shaker and the impulse hammer head. The force sensor is used for recording the applied load to the structure. An amplifier (Type 2693) from Bruel Kjaer and a power amplifier (Type 50,009) from TIRA have been used for the force sensor and the shaker, respectively.