## 3 Shock Experiment and Simulation Study of Spacecraft Structure
### Hybrid FE-SEA Model and Solution  
The typical spacecraft structure used in the experiment is shown in Figure 3. The hybrid FE-SEA model of the structure is established based on FE-SEA theory, as shown in Figure 8.  
Figure 8: The hybrid FE-SEA model of spacecraft structure. Figure 7: The _STFT_ results of shock load signal. In the typical structure, the aluminum honeycomb sandwich panels behave with low stiffness but high modal density. This accords with the characteristics of SEA. So, the aluminum honeycomb sandwich panels are built as SEA model. The modal density of the connecting beam is low. It is built as a FE model. The process of model establishment meets the accuracy requirements of simplification and equivalence. The beam structure is made of cylindrical aluminum alloy, with a length of 110 cm and a density of 2750 kg/m\({}^{3}\). The finite element model of the beam structure is established, according to the beam structure form in Figure 3, with a mass of 4.3 kg. The plate structure is an aluminum honeycomb sandwich plate structure; the size is 100 cm \(\times\) 120 cm, and the thickness is 3 cm. The thickness of the upper and lower aluminum plates is 0.1 cm, and the density is 2700 kg/m\({}^{3}\). The thickness of honeycomb sandwich structure is 2.8 cm, and the density is 48 kg/m\({}^{3}\). The statistical energy analysis model of sandwich structure is established according to the actual structure, and the mass is 8.2 kg. Since the honeycomb panel and the beam structure are connected by screws, a mixed point connection is established between the FE subsystem and the SEA subsystem. In VAone, corresponding material attributes are generated, according to material type settings. In the early stage, we conducted the parameter test of a single-plate, double-plate and four-plate structure. The internal loss factor, coupling loss factor and modal density of SEA model are obtained through typical structural parameter measurement experiments. As shown in Figure 8, the plate shocked by the load and the three response plates are defined as plate 1, plate 2, plate 3 and plate 4, respectively. For the statistical energy analysis subsystem, only the modal characteristics of the structure need to be concerned. In the process of modeling, the form of the structure is simplified. After the SEA model is established, the modal density of the subsystem in each frequency band is detected based on the VAone intermediate frequency band modal number analysis. Based on hybrid connection detection, the connection mode between subsystems is modified. The modal number of SEA subsystem in each frequency band is greater than five. The SEA model meets the calculation standard. The parameters of hybrid connection are corrected by a parameter test. The convergence and stability of the finite element subsystem are analyzed. The overall modal density of the finite element subsystem is low. So, the number of grids meets the requirements of calculation accuracy. The vibration mode of finite element structure is consistent with that of an actual beam structure. Therefore, the model based on hybrid method can effectively characterize the actual structure. The prediction of structural shock response based on the model is reasonable and effective. Taking the time-frequency analysis results as the input load, the quasi-steady state loading mode is used to calculate the coupled plate structure. The loading mode of the force spectrum is used, and the result of the structural response is predicted based on the hybrid FE-SEA method. By using the phase information and a series of frequency response, the time domain response is reconstructed by utilizing the ISTFT technique. The results of the overall time domain response are reconstructed. The \(SRS\) of typical spacecraft structure can be calculated based on the time domain response results. So far, we obtain the final shock response of the structure based on the hybrid FE-SEA method.