## 3 Design of the Test Specim  
The design of the wind turbine stator (WTS) test specimen for laboratory purposes should resemble the real-world scenario in a very close manner. Therefore, the decision on the WTS test specimen and HCDP design was taken collectively with the Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM-Dresden and with the industrial partner. The selection of granular materials for the experimental study was also taken together with the project partners. The generator is one of the essential subsystems of a wind turbine and is used for converting mechanical energy into electrical energy. In general, the generator consists of two major parts, namely: rotor and stator. The stator of an annular wind turbine generator comprises of a big ring (stator ring) and several arms (stator arm). The stator arms are made up of hollow sections and are connected to the ring to provide support to the whole structure, see Figure 1. Normally, a stator ring contains electromagnetic coils that create an electromagnetic field when current flows through it. The electromagnetic interaction between stator and spinning poles is responsible for generating mechanical vibrations in the generator. The vibration produced in the generator is transmitted to the other structures and then is radiated into the surrounding. The current contribution aims to damp the vibration transmission by using the HCDP concept based on granular material damping properties. To investigate the efficiency of the HCDP concept, the stator of a wind turbine annular generator is chosen. The hollow sections of the stator ring and arms make the assembling feature of HCDP to WTS components more convenient. Furthermore, the aim is to reduce the vibration amplitude near the stator arm and ring so that the unwanted disturbance in the structure does not travel further. To study the above mentioned idea experimentally, a WTS test specimen is required. The primary idea for laboratory test specimen design was to manufacture the replica of the original WTS, as shown on the left side of Figure 1, and then to scale it down by a particular factor that can make the WTS test specimen handling easy. Scaling the entire stator also requires simultaneous scaling of the HCDP geometry including wall thickness and core sizes. This can lead to very small HDCP cavities, which are not possible to manufacture. Moreover, the movement of the granular material will be also restricted due to the tiny core sizes. In addition, scaling the wall thickness of honeycomb cores further can make the HCDP structure weak against mechanical deformation. Therefore, in the previous study [38], numerical modal analysis were performed on different WTS test specimen profile with respect to their vibroacoustic behavior. The numerical study aimed to obtain a similar number of eigenmodes below 355 Hz as in the case of the original wind turbine generator. It had been concluded that the WTS test specimen can be designed by taking a small section of the original wind turbine stator and scale it down, see Figure 1. The WTS test specimen consists of two parts, i.e., stator arm and stator ring, see Figure 1. Several holes are drilled on each side of the stator ring wall and stator arm base. Each component of the WTS test specimen is assembled with the help of screws, see Figure 1. The geometrical parameters of the WTS specimen is taken from a previous study [38]. The WTS specimen is made up of steel as it is also in the case of the original wind turbine stator. The HCDP consists of two thin face sheets, top and bottom face sheets, respectively. These face sheets are attached to a lightweight honeycomb core through the bonding process, see Figure 2. The HCDP face sheets and cores are made up of Aluminium to keep the additional mass as low as possible. The geometrical parameters of the honeycomb core profiles are discussed in the previous study [38]. Altogether, seven HCDPs with the same length, width, and core height are manufactured at the IFAM-Dresden.