# Research on Decision-Making Methods for Autonomous Navigation in Inland Tribitary Waterways
## 3 Methodology
### Collision Avoidance Decision-Making Model
To address this complexity, a decomposition approach is proposed, wherein multi-ship encounters are reduced to multiple two-ship encounter subproblems. This analytical simplification facilitates focused investigation of pairwise collision avoidance strategies while streamlining the resolution of collision avoidance challenges. The prioritization of avoidance targets is achieved through comparative collision risk identification between the OS and TS. The operational framework mandates that evasive actions must either prioritize avoidance of the highest-risk vessel without inducing secondary collision risks or eliminate collision risks with all TSs through a single coordinated maneuver. Notably, the RPRCIRCA do not necessitate maximum evasive actions but emphasize constrained optimization under navigational limitations. Given the spatial constraints of inland waterways, excessive steering maneuvers are prohibited to ensure navigational safety and efficiency. Empirical evidence from inland navigation practices supports the imposition of a maximum permissible steering angle range of \(\theta=[-45^{\circ},45^{\circ}]\). This angular restriction maintains ship stability during collision avoidance maneuvers while preventing emergent risks with external obstacles or adjacent ships. The two-dimensional solution space \(\zeta=\{\theta,T\}\) integrates course alteration (\(\theta\)) and engine telegraph adjustments (\(T\)), where  
Figure 14: Relationship between motion vectors and safe collision avoidance. \(T\) represents engine speed reductions relative to current operational levels. Through ship motion modeling and control systems, theoretical solutions are translated into executable commands \(m(W,T)\). \[m(W,T)= \begin{bmatrix}(W_{1},T_{1}),\ldots,(W_{1},T_{n})\\ \ldots\\ (W_{m},T_{1}),\ldots,(W_{m},T_{n})\end{bmatrix}  \tag{22}\]  
Different telegraphing corresponds to different propeller RPM (Revolutions Per Minute), and the RPM of the propeller is controlled to realize the variable speed control of the ship. According to the general ship speed change performance, the change rate of propeller RPM is generally 0.2 r/s, that is, 1 RPM is increased or decreased every 5 s. According to the current ship propeller RPM \(T_{O}\) and the target propeller RPM T, the propeller RPM \(T_{t}\) after time \(t\) can be obtained. If the current RPM \(T_{t}\) has reached the maximum or minimum RPM, it will not increase or decrease. \[T_{t}= \begin{cases}T_{O}-0.2t,\;if\;T<T_{O}\\ T_{O}+0.2t,\;if\;T>T_{O}\end{cases}  \tag{23}\]  
The decision-making protocol incorporates navigational rule constraints through situational filtering. For instance, in starboard crossing scenarios, course alteration is restricted to \(\theta=[0^{\circ},45^{\circ}]\). Computational simulations based on ship motion models project spatiotemporal trajectories under various \(m(W,T)\) combinations. Then, based on the mathematical model of ship motion, the change process of the ship's motion vector under different maneuvering combination schemes is calculated, and the position of TSs at the same time can be obtained based on each TS's motion situation. Through the spatiotemporal evolution relationship between the OS and the TSs, combined with the ship domain model, the maneuvering scheme that can enable TSs to pass from the outside of the OS's ship domain is judged, which is the safe collision avoidance decision-making scheme under the current multi-objective encounter situation.