# CFD Simulation of the Safety of Unmanned Ship Berthing under the Influence of Various Factors
## 4 Conclusions  
CFD modeling and simulation were carried out in this study for the berthing of an unmanned ship as follows.  
(1) To explore and establish a CFD model of unmanned ship navigation with multi-factors' influence, we performed a CFD simulation. The results showed that the total resistance of the hull against the current can be 1.60 times higher compared to the downstream resistance. The unmanned ship has a resistance of 1.16 N at 0.45 m/s and 67.05 N at 5.45 m/s. Water flow resistance is the dominant factor, accounting for more than 80% of the total resistance.  
Figure 10: The wind characteristics of 0, 45, 90, and 180 degrees at wind speeds of 20 m/s.  
(2) When changing the distance between ship and shore at fixed speed, the torque change was calculated. We found that the torque is small, but the growth rate is very large when driving below 2 m/s, and the torque growth rate is stable above 2 m/s.  
(3) Based on the established coupling model, a multi-factor berthing safety study is carried out on an actual unmanned ship. The results shown that when the speed increases from 4 m/s to 12 m/s, the curve slope is small, the resistance increases from 3666 N to 18,056 N, and the rear slope increases. At 4 m/s, the maximum pressure of the unmanned bow is 6874 N, the pressure increases with the speed, and when the speed is 24 m/s, the maximum pressure is up to 238,869 Pa. By comparing water resistance with wind resistance, we can know that water resistance accounts for the main part. When the wind speed is fixed, the vertical force of the unmanned ship increases first and then decreases to zero and then reverses the same law change, and the maximum resistance is about 425 N at the wind angle of about 45 degrees; At 90 degrees, the maximum lateral force on an unmanned boat is about 638 N.  
The above results give the characteristics of speed field, pressure field and vortex under different speed, wind direction and shore wall distance, reveal the coupling characteristics of unmanned ship berthing navigation and wind and wave environment disturbance, which can provide control strategy for unmanned ship berthing safety, and provide theoretical basis for unmanned ship route planning and obstacle avoidance, safety design, etc.  
Conceptualization, G.X.; methodology, G.X.; software, S.G.; validation, C.T. and G.X.; formal analysis, G.X.; investigation, S.G. and Y.W.; resources, X.H.; data curation, S.G. and Y.W.; writing--original draft preparation, S.G. and G.X.; writing--review and editing, X.H. and G.X.; visualization, S.G.; supervision, X.H.; project administration, X.H. and B.S.; funding acquisition, G.X., X.H. and B.S. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Guangdong Basic and Applied Basic Research Foundation (2021A1515010794), Guangdong Provincial Key Laboratory of Electronic Information Products Reliability Technology (2017B030314151), Guangdong Province Science and Technology project (2018B010109004 and 2018B010109005), Guangzhou Science and Technology project (201704020052, 201802020021 and 201802020009), Guangdong Marine Economy Promotion projects Fund (GDOE (2019) A13).  
The authors declare no conflict of interest.