## 6 Conclusions  
The identification of the mechanical parameters of the viscoelastic core layer is of great significance for the modeling of a viscoelastically damped structure and vibration reduction design. An identification method based on the obtained frequency sweeping response of a composite structure was proposed in this study and the relevant conclusions are listed as follows.  
1. In the created vibration response analysis model of the CLD plate, both the material damping and the remaining equivalent viscous damping were considered. This kind of damping model is consistent with the real environment of the CLD plate, which is helpful to improve the identification accuracy of the material parameters of the viscoelastic core layer.
2. The method in which the sweeping frequency response under base excitation is mainly used to identify the mechanical parameters of the viscoelastic core layer was proposed. This identification method avoids the difference caused by the inaccurate location of the exciting point in the hammer test. On the other hand, it can also reduce the interference of noise seen in the identification results to the maximum extent.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameters** & \(\mathbf{G_{0}}\) & \(\mathbf{G_{\infty}}\) & **o** & **ff** \\ \hline Identified value & 0.27 MPa & 4.1 MPa & \(1.21\times 10^{-4}\) & 0.83 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Parameters of the fractional derivative model of ZN_1.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Frequency Point (Hz)** & **Experiment (\(\mathbf{R_{e}}\))** & **Theoretical Calculation (\(\mathbf{R_{t}}\))** & **Difference \(|\mathbf{R_{t}}-\mathbf{R_{e}}|/\mathbf{R_{e}}\)** \\ \hline
18.4 & 0.0726 & 0.0708 & 2.48 \\
19.3 * & 0.1112 & 0.1128 & 1.44 \\
20.2 & 0.0705 & 0.0729 & 3.40 \\
94.3 & 0.0197 & 0.0206 & 4.57 \\
100.5 * & 0.0279 & 0.0276 & 1.08 \\
105.0 & 0.0240 & 0.0229 & 4.58 \\
264.8 & 0.0082 & 0.0086 & 4.87 \\
281.1 * & 0.0107 & 0.0109 & 1.58 \\
295.2 & 0.0092 & 0.0088 & 4.99 \\ \hline \hline \end{tabular} Notation: symbol * refers to resonance point.  
\end{table}
Table 5: Vibration responses obtained by theoretical calculations and the experiment/(m/s).  
3. Taking the minimum differences between the theoretical and experimental values of the vibration response as the objective function, a matching calculation based on sensitivity was proposed. On the premise of obtaining a reasonable initial value, the parameters of the viscoelastic core layer to be identified can quickly converge.
4. The CLD plate with ZN_1 viscoelastic material as the core layer was chosen to demonstrate the developed method. The identified viscoelastic mechanical parameters were substituted into the analysis model and the predicted vibration response was compared with the experimental values. The rationality of the identification results was verified.  
This project was supported by the Fundamental Research Funds for the Central Universities of China (Grant No. N150304008 and N140301001).  
[PERSON] and [PERSON] carried out the theoretical calculations and experiments; [PERSON] analyzed the data; [PERSON] derived the equation of motion of CLD structure; [PERSON] and [PERSON] wrote the paper.  
The authors declare no conflict of interest.