# CFD Simulation of the Safety of Unmanned Ship Berthing under the Influence of Various Factors
## 1 Introduction  
Unmanned ships are widely used in marine exploration and development, island reef resupply, marine environmental monitoring, improving the energy efficiency and environmental performance of ports and terminals [1]. In unmanned ships, miniaturization, intelligent direction of development [2, 3], lack of dock dynamic berthing are pursued; Berthing is affected by the shallow water effect, the shore wall effect, as well as by navigation, speed, speed reduction, wind speed, and wind direction, and other factors [4, 5, 6, 7, 8]. Automatic berthing is not an easy task because of various factors, such as the non-linearity of the low-speed maneuvering model, danger of collision with the berth, etc. [9]. Unmanned ship movement state is difficult to determine; during movement; berthing maneuverability becomes more difficult, stranding, grounding, collision, and other accidents can occur, and it will be difficult to recover losses. Therefore, research on dynamic berthing require algorithms or unmanned ship positioning, avoidance, and manipulation [10, 11]. The reduced speed during the berthing of unmanned ships results in a decrease in maneuvering performance. At present, the main research methods for berthing motion are the empirical formula estimation, the maneuvering test method, the hydrodynamic CFD simulation and the combination of these methods [12; 13; 14]. A limited number of experimental cases are available in the literature. Consequently, the ability to reliably predict the hull forces (and the related hydrodynamic coefficients) via computational fluid dynamics calculations may represent a significant added value to further tune or to generate new simplified hull forces models to be employed in a maneuvering code [15]. The empirical formula estimation method is limited by the ship type and live ship test data used in the establishment of the database. A manipulative test requires a ship's towing tank, has high cost, and is subject to the scale effect. The CFD method has gradually become the main means to study the hydrodynamics of ship berthing because of its advantages of low computational cost, short cycle, and high calculation accuracy [16; 17; 18; 19; 20]. Unmanned ship movement is affected by many factors, and the method of calculation of unmanned ship wind and wave coupling CFD mainly includes direct simulation, large vortex simulation, and solving the Reynolds average Navier-Stokes (RANS) equation. A CFD numerical simulation of the calculation error and uncertainty was carried out by [PERSON] and others [21]. Some researchers have also verified and confirmed the calculation method of the ship's viscous flow [22; 23; 24; 25]. A systematic application of the open-source viscous-based flow solver OpenFOAM to predict forces at low-speed maneuvering conditions for two ship test cases (the Korea container ship (KCS)) and the (Korea very large crude carrier (KVLCC)) was presented [15]. In the study of berthing hydrodynamics of large ships, [PERSON] and others adopted the CFD method to study the safety of ships with flowing berths in gravity whaves through the standard ship model series 60 approved by the International Towing Tank Conference (ITTC). The berthing process passed the verification of the ship's towing tank test results [26]. [PERSON] and [PERSON] used the explicit finite non-linear element method and a measurement technology to simulate the collision process between ship berthing and wharf. Based on the maximum stress and fender deformation limit of the component, they obtained a safe berthing of ships with different displacements. The maximum berthing speed provides guidance for the berthing speed control of ships [27].