## 4 Conclusions  
In general, only static loads are considered in a structural analysis at the design stage. The document in the Compressed Gas Association (CGA) TB-25: Design Considerations for Tube Trailers presents the static loading considerations. This document contains design criteria for mounting tubes to tube adapters and skid structures to withstand the total  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Driving Course** & **Maximum Von Mises Stress** & \
\begin{tabular}{c} **Safety Factor Compared to** \\ **Yield Strength** \\ \end{tabular} &
\begin{tabular}{c} **Safety Factor Compared to** \\ **Ultimate Tensile Strength** \\ \end{tabular} \\ \hline Flat course & 0.42 MPa & 595.24 & 952.38 \\ Pothole course & 160.46 MPa & 1.56 & 2.49 \\ Short-wave course & 210.83 MPa & 1.19 & 1.90 \\ Long-wave course & 52.10 MPa & 4.80 & 7.68 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Safety factors according to the driving course.  
Figure 12: Maximum deformation result under pothole course.  
load, including tubes and adapters. In this study, in order to increase the reliability of the skid structure, the integrity of the structure was evaluated by considering the dynamic load received when driving on a special durable road. The dynamics of the driving trailer according to the irregularities of the road surface were obtained through multibody dynamic simulations considering the full car model equipped with 64 hydrogen tubes. The driving road conditions of the trailer were divided into four different driving courses, i.e., flat, pothole, short wave, and long wave. The road conditions utilized in this study were modeled using the special endurance roads of the actual driving test site (Korea Automobile Testing & Research Institute) specifications. Although there are various road conditions, the three road conditions considered in this study are most common on roads and have a significant influence on the integrity of a skid structure. The flat road was simulated as a reference to verify the trailer analysis model.  
The transient structural analysis of the skid was performed by considering the resulting acceleration values at the corners of the skid as constraints. According to the comparison of the stress analysis results, we can conclude that the maximum von Mises stress is highly correlated with the acceleration period. It is considered that the sequential simulation process presented in this study could be widely applied to the structural safety assessment of a tube skid mounted on a trailer for hydrogen transportation in the early stage of design.  
Conceptualization, S.K. and H.-L.J.; methodology, S.K. and J.K.; software, H.K. ([PERSON]), B.K., and K.C.; validation, S.K. and H.-L.J.; formal analysis, S.K.; investigation, S.K., J.J., and H.K. ([PERSON]); resources, S.K. and B.K.; data curation, H.K. ([PERSON]) and K.C.; writing--original draft preparation, S.K.; writing--review and editing, S.K. and H.-L.J.; visualization, S.K.; supervision, H.-L.J.; project administration, H.K. ([PERSON]); funding acquisition, H.-L.J. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Technology Innovation Program (no. 20003058, Development of Hydrogen Gas Charging system for decreasing by half of FCEV Bus charging time and increasing two times of Hydrogen gas Tube Trailer transport capacity) funded by the Ministry of Trade, Industry and Energy (MOTIE, Korea).  
Not applicable.  
The authors declare no conflict of interest.