# The Subsea Micro-Drilling Vehicle's Dynamic Analysis during Landing
## 3 Simulation Analysis of Landing Dynamics  
### SMDV Landing Response Analysis  
This study examines the center of mass displacement and center of mass acceleration response of the SMDV to evaluate its security. The center-of-mass displacement of the SMDV corresponds to the sinkage of its impact on the subsea substrate, which can be used to analyze whether it affects subsequent driving. The center-of-mass acceleration of the SMDV can be used to analyze the impact resistance of the instrumentation in the SMDV, and Figure 6 depicts the flowchart of the simulation method. Regarding a vehicle lowered from a height of 2 m onto a flat substrate surface, the simulation analysis of the substrate impact of the SMDV is performed, and the results are depicted in Figures 7-9. The process of SMDV landing on the subsea substrate can be divided into three phases based on the changes in velocity, acceleration, and the angle between the SMDV and the subsea substrate. The first stage occurred from 0-1 seconds when the SMDV center-of-mass displacement, velocity, and acceleration experienced their respective maxima. The maxima of the angle between the SMDV and the substrate surface occurred from 0-1.5 s: the maximum subsidence value of 336.28 mm, the maximum velocity of about 4.24 m/s, the maximum acceleration of 63.5 m/s\({}^{2}\) appeared at about 0.7 s, and the maximum angle of clamping of 6.2\({}^{\circ}\) appeared at about 1.3 s. The second stage occurred from 1-2 s, and the SMDV's center of mass displacement, velocity, and acceleration oscillated and altered  
Figure 5: Relationship between landing speed and release fall height (in air/below water). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Data Type** & **Parameter** & **Values** \\ \hline coefficient of water resistance & \(C_{d}\) & 1.0 \\ waterfront area (m\({}^{2}\)) & \(A\) & 1.67 \\ SMDV volume (m\({}^{3}\)) & \(V\) & 0.169 \\ Density of seawater (kg/m\({}^{3}\)) & \(\rho\) & 1037 \\ Speed of falling motion & \(v\) & / \\ Weight (in air) & \(m\) & 2000 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Hydrodynamic coefficient values. before stabilizing after approximately eight cycles. The angle between the SMDV and the substrate surface stabilized after three cycles. After two seconds, the displacement, velocity, and acceleration of the SMDV's center of mass and the angle between the SMDV and the substrate surface were essentially stable, with a subsidence value of 325.07 mm, and the velocity and acceleration were 0. Since the SMDV's center of mass was in front of the SMDV, the body of the SMDV was slightly inclined forward when it was stabilized, forming an angle of \(-1.5^{\circ}\) with the substrate surface. Figure 6: Flow chart of the simulation method. Figure 8: Simulation curve of SMDV mass velocity and sinkage. Figure 7: SMDV Landing sinking process. Figure 9: Simulation curve of SMDV-to-substrate angle and mass acceleration. To observe the effect of the release height of the SMDV on its subsidence and impact acceleration, simulation experiments of the SMDV at 2-5 m release height were conducted in RecurDyn software, which was set up with the equivalent height of the free-fall equivalent to obtain the subsidence (stable value) and impact acceleration (maximal value) of the SMDV at different release heights, as illustrated in Figure 10. As shown in the graph, as the SMDV's release height increases, its lowering volume and impact acceleration increase approximately linearly, consistent with the upward trend of the SMDV's landing speed. In general, when the landing sinkage of the SMDV does not exceed the distance between the top of the drive wheel and the substrate surface of the track (350 mm for SMDV), the tracked traveling mechanism can travel after landing. The simulation results show that when the release height is 5 m, the sinkage amount of the SMDV is close to the critical value.