## 6 Discussion  
In this study, an innovative method for the vibration damping of the near-bit MWD is proposed for use in the field of pneumatic DTH hammer drilling. The vibration-damping system designed using this method is highly stable. It can achieve an optimal vibration-damping effect concerning the mass and excitation frequency of the MWD, which significantly improves the accuracy and service life of the MWD in the drilling process. Meanwhile, the parameter optimization method based on NSGA-II is used to solve the optimal damping parameters. The method not only significantly improves the computational efficiency of the damping system design but also enhances the variety of parameter choices and the accuracy of the optimization results. Thus, this study provides a highly efficient and reliable vibration-damping solution for pneumatic DTH hammer drilling projects.  
However, there are some shortcomings in this research process:  
1. The lower impact of transverse and torsional vibrations was neglected: In the investigation of the vibration characteristics of the circuit unit, this study mainly considered the impact of longitudinal vibrations and simplified or neglected torsional and transverse vibrations, as well as the three kinds of vibration coupling effects. These vibrations will have a certain impact on the vibration-damping performance of the vibration-damping device. Despite the fact that the simulation experiment process shows a good vibration-damping effect, the effect of this coupled vibration on the vibration-damping device has not yet been fully investigated in relation to the practical applications concerning impact. Further studies are needed to investigate the interference of the torsional vibrations of the drill string and its coupling with transverse vibrations on the damping device.
2. Differences between the simplified model and the actual working conditions: This study establishes a forced vibration response model of a circuit unit by studying the vibration characteristics of a drill string near a drill bit and finds the optimal damping parameters of a damping system. However, many uncertainties concerning the actual drilling process may have an impact on the performance of the vibration-damping system, such as formation changes, fluctuations in drilling fluid performance, etc.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Level**} & \multirow{2}{*}{**Peak Difference**} & \multirow{2}{*}{**Peak Attenuation Rate**} & \multicolumn{2}{c}{**Fluctuation Rate**} & \multirow{2}{*}{**System Stability**} \\  & & & **Rate** & & **Before** & **After** & **Enhancement Rate** \\ \hline
10 g & 8.988 & 94.710\% & 1.345 & 0.085 & 93.660\% \\
15 g & 13.906 & 91.978\% & 2.707 & 0.247 & 90.862\% \\
20 g & 20.598 & 94.816\% & 2.346 & 0.374 & 84.053\% \\
30 g & 26.938 & 86.549\% & 5.932 & 0.704 & 88.132\% \\
40 g & 34.750 & 90.938\% & 6.975 & 0.738 & 89.413\% \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparison of data before and after damping in five groups of experiments with different levels at the same frequency.  
These factors are not fully reflected in the model. Future research work will address these shortcomings and consider more practical working condition factors to further improve and optimize the model in order to achieve more accurate and reliable vibration damping.